https://bugs.gentoo.org/870412
https://git.savannah.gnu.org/cgit/autoconf.git/commit/?id=8b5e2016c7ed2d67f31b03a3d2e361858ff5299b

Backport the K&R decls fix to 2.13 to avoid configure tests
failing (often "silently", i.e. doesn't fail the build of
the package overall, just leads to wrong results) with
newer compilers like the upcoming Clang 16.

From d8ad1096be4352c588b9bc1e16b6758f4f32b96a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Arsen=20Arsenovi=C4=87?= <arsen@aarsen.me>
Date: Mon, 19 Sep 2022 01:38:29 +0200
Subject: [PATCH] ac{general,specific}: declare void param lists, where apt

--- a/acgeneral.m4
+++ b/acgeneral.m4
@@ -1542,7 +1542,7 @@ extern "C"
 ])dnl
 [/* We use char because int might match the return type of a gcc2
     builtin and then its argument prototype would still apply.  */
-char $1();
+char $1(void);
 ]),
 [$1()],
 [$2],
@@ -1597,7 +1597,7 @@ extern "C"
 ])dnl
 [/* We use char because int might match the return type of a gcc2
     builtin and then its argument prototype would still apply.  */
-char $2();
+char $2(void);
 ])),
 	    [$2()],
 	    eval "ac_cv_lib_$ac_lib_var=yes",
@@ -1733,7 +1733,7 @@ dnl [#]line __oline__ "[$]0"
 [#]line __oline__ "configure"
 #include "confdefs.h"
 [$1]
-int main() {
+int main(void) {
 [$2]
 ; return 0; }
 ])EOF
@@ -1777,7 +1777,7 @@ dnl [#]line __oline__ "[$]0"
 [#]line __oline__ "configure"
 #include "confdefs.h"
 [$1]
-int main() {
+int main(void) {
 [$2]
 ; return 0; }
 ])EOF
@@ -1934,7 +1934,7 @@ extern "C"
 ])dnl
 [/* We use char because int might match the return type of a gcc2
     builtin and then its argument prototype would still apply.  */
-char $1();
+char $1(void);
 ], [
 /* The GNU C library defines this for functions which it implements
     to always fail with ENOSYS.  Some functions are actually named
@@ -1988,7 +1988,7 @@ changequote([, ])dnl
 AC_MSG_CHECKING(size of $1)
 AC_CACHE_VAL(AC_CV_NAME,
 [AC_TRY_RUN([#include <stdio.h>
-main()
+main(void)
 {
   FILE *f=fopen("conftestval", "w");
   if (!f) exit(1);
--- a/acspecific.m4
+++ b/acspecific.m4
@@ -202,7 +202,7 @@ AC_DEFUN(AC_PROG_CC_WORKS,
 [AC_MSG_CHECKING([whether the C compiler ($CC $CFLAGS $LDFLAGS) works])
 AC_LANG_SAVE
 AC_LANG_C
-AC_TRY_COMPILER([main(){return(0);}], ac_cv_prog_cc_works, ac_cv_prog_cc_cross)
+AC_TRY_COMPILER([int main(void){return(0);}], ac_cv_prog_cc_works, ac_cv_prog_cc_cross)
 AC_LANG_RESTORE
 AC_MSG_RESULT($ac_cv_prog_cc_works)
 if test $ac_cv_prog_cc_works = no; then
@@ -217,7 +217,7 @@ AC_DEFUN(AC_PROG_CXX_WORKS,
 [AC_MSG_CHECKING([whether the C++ compiler ($CXX $CXXFLAGS $LDFLAGS) works])
 AC_LANG_SAVE
 AC_LANG_CPLUSPLUS
-AC_TRY_COMPILER([int main(){return(0);}], ac_cv_prog_cxx_works, ac_cv_prog_cxx_cross)
+AC_TRY_COMPILER([int main(void){return(0);}], ac_cv_prog_cxx_works, ac_cv_prog_cxx_cross)
 AC_LANG_RESTORE
 AC_MSG_RESULT($ac_cv_prog_cxx_works)
 if test $ac_cv_prog_cxx_works = no; then
@@ -300,7 +300,7 @@ fi])])
 
 AC_DEFUN(AC_PROG_CC_G,
 [AC_CACHE_CHECK(whether ${CC-cc} accepts -g, ac_cv_prog_cc_g,
-[echo 'void f(){}' > conftest.c
+[echo 'void f(void){}' > conftest.c
 if test -z "`${CC-cc} -g -c conftest.c 2>&1`"; then
   ac_cv_prog_cc_g=yes
 else
@@ -311,7 +311,7 @@ rm -f conftest*
 
 AC_DEFUN(AC_PROG_CXX_G,
 [AC_CACHE_CHECK(whether ${CXX-g++} accepts -g, ac_cv_prog_cxx_g,
-[echo 'void f(){}' > conftest.cc
+[echo 'void f(void){}' > conftest.cc
 if test -z "`${CXX-g++} -g -c conftest.cc 2>&1`"; then
   ac_cv_prog_cxx_g=yes
 else
@@ -371,7 +371,7 @@ changequote(, )dnl
 		       sed -e 's/[^a-zA-Z0-9_]/_/g' -e 's/^[0-9]/_/'`"
 changequote([, ])dnl
 AC_CACHE_VAL(ac_cv_prog_cc_${ac_cc}_c_o,
-[echo 'foo(){}' > conftest.c
+[echo 'foo(void){}' > conftest.c
 # Make sure it works both with $CC and with simple cc.
 # We do the test twice because some compilers refuse to overwrite an
 # existing .o file with -o, though they will create one.
@@ -709,7 +709,7 @@ AC_TRY_RUN([#include <ctype.h>
 #define ISLOWER(c) ('a' <= (c) && (c) <= 'z')
 #define TOUPPER(c) (ISLOWER(c) ? 'A' + ((c) - 'a') : (c))
 #define XOR(e, f) (((e) && !(f)) || (!(e) && (f)))
-int main () { int i; for (i = 0; i < 256; i++)
+int main (void) { int i; for (i = 0; i < 256; i++)
 if (XOR (islower (i), ISLOWER (i)) || toupper (i) != TOUPPER (i)) exit(2);
 exit (0); }
 ], , ac_cv_header_stdc=no, :)
@@ -820,7 +820,7 @@ esac
 AC_CACHE_CHECK(whether closedir returns void, ac_cv_func_closedir_void,
 [AC_TRY_RUN([#include <sys/types.h>
 #include <$ac_header_dirent>
-int closedir(); main() { exit(closedir(opendir(".")) != 0); }],
+int closedir(...); int main(void) { exit(closedir(opendir(".")) != 0); }],
   ac_cv_func_closedir_void=no, ac_cv_func_closedir_void=yes, ac_cv_func_closedir_void=yes)])
 if test $ac_cv_func_closedir_void = yes; then
   AC_DEFINE(VOID_CLOSEDIR)
@@ -911,7 +911,7 @@ changequote(<<, >>)dnl
 #define NGID 256
 #undef MAX
 #define MAX(x, y) ((x) > (y) ? (x) : (y))
-main()
+int main(void)
 {
   gid_t gidset[NGID];
   int i, n;
@@ -973,7 +973,7 @@ AC_DEFUN(AC_TYPE_SIGNAL,
 #ifdef __cplusplus
 extern "C" void (*signal (int, void (*)(int)))(int);
 #else
-void (*signal ()) ();
+void (*signal (void)) (void);
 #endif
 ],
 [int i;], ac_cv_type_signal=void, ac_cv_type_signal=int)])
@@ -989,7 +989,7 @@ AC_DEFUN(AC_FUNC_CLOSEDIR_VOID,
 AC_CACHE_CHECK(whether closedir returns void, ac_cv_func_closedir_void,
 [AC_TRY_RUN([#include <sys/types.h>
 #include <$ac_header_dirent>
-int closedir(); main() { exit(closedir(opendir(".")) != 0); }],
+int closedir(...); int main(void) { exit(closedir(opendir(".")) != 0); }],
   ac_cv_func_closedir_void=no, ac_cv_func_closedir_void=yes, ac_cv_func_closedir_void=yes)])
 if test $ac_cv_func_closedir_void = yes; then
   AC_DEFINE(CLOSEDIR_VOID)
@@ -1001,7 +1001,7 @@ AC_DEFUN(AC_FUNC_FNMATCH,
 # Some versions of Solaris or SCO have a broken fnmatch function.
 # So we run a test program.  If we are cross-compiling, take no chance.
 # Thanks to John Oleynick and Franc,ois Pinard for this test.
-[AC_TRY_RUN([main() { exit (fnmatch ("a*", "abc", 0) != 0); }],
+[AC_TRY_RUN([int main(void) { exit (fnmatch ("a*", "abc", 0) != 0); }],
 ac_cv_func_fnmatch_works=yes, ac_cv_func_fnmatch_works=no,
 ac_cv_func_fnmatch_works=no)])
 if test $ac_cv_func_fnmatch_works = yes; then
@@ -1083,11 +1083,11 @@ AC_CACHE_CHECK(for working mmap, ac_cv_func_mmap_fixed_mapped,
 #ifdef __cplusplus
 extern "C" { void *malloc(unsigned); }
 #else
-char *malloc();
+char *malloc(...);
 #endif
 
 int
-main()
+main(void)
 {
 	char *data, *data2, *data3;
 	int i, pagesize;
@@ -1172,7 +1172,7 @@ int     pid;
 int     pg1, pg2, pg3, pg4;
 int     ng, np, s, child;
 
-main()
+int main(void)
 {
         pid = getpid();
         pg1 = getpgrp(0);
@@ -1228,7 +1228,7 @@ AC_TRY_RUN([
  * If this system has a BSD-style setpgrp, which takes arguments, exit
  * successfully.
  */
-main()
+int main(void)
 {
     if (setpgrp(1,1) == -1)
 	exit(0);
@@ -1291,7 +1291,7 @@ sparc_address_test (arg) int arg;
     }
   }
 }
-main() {
+int main(void) {
   pid_t parent = getpid ();
   pid_t child;
 
@@ -1360,7 +1360,7 @@ AC_DEFUN(AC_FUNC_WAIT3,
 #include <sys/resource.h>
 #include <stdio.h>
 /* HP-UX has wait3 but does not fill in rusage at all.  */
-main() {
+int main(void) {
   struct rusage r;
   int i;
   /* Use a field that we can force nonzero --
@@ -1416,7 +1416,7 @@ AC_CACHE_CHECK([for alloca], ac_cv_func_alloca_works,
  #pragma alloca
 #   else
 #    ifndef alloca /* predefined by HP cc +Olibcalls */
-char *alloca ();
+char *alloca (...);
 #    endif
 #   endif
 #  endif
@@ -1464,7 +1464,7 @@ AC_CACHE_CHECK(stack direction for C alloca, ac_cv_c_stack_direction,
   else
     return (&dummy > addr) ? 1 : -1;
 }
-main ()
+int main (void)
 {
   exit (find_stack_direction() < 0);
 }], ac_cv_c_stack_direction=1, ac_cv_c_stack_direction=-1,
@@ -1582,7 +1582,7 @@ AC_DEFUN(AC_FUNC_UTIME_NULL,
 # Sequent interprets utime(file, 0) to mean use start of epoch.  Wrong.
 AC_TRY_RUN([#include <sys/types.h>
 #include <sys/stat.h>
-main() {
+int main(void) {
 struct stat s, t;
 exit(!(stat ("conftestdata", &s) == 0 && utime("conftestdata", (long *)0) == 0
 && stat("conftestdata", &t) == 0 && t.st_mtime >= s.st_mtime
@@ -1598,7 +1598,7 @@ fi
 AC_DEFUN(AC_FUNC_STRCOLL,
 [AC_CACHE_CHECK(for working strcoll, ac_cv_func_strcoll_works,
 [AC_TRY_RUN([#include <string.h>
-main ()
+int main (void)
 {
   exit (strcoll ("abc", "def") >= 0 ||
 	strcoll ("ABC", "DEF") >= 0 ||
@@ -1615,7 +1615,7 @@ AC_DEFUN(AC_FUNC_SETVBUF_REVERSED,
   ac_cv_func_setvbuf_reversed,
 [AC_TRY_RUN([#include <stdio.h>
 /* If setvbuf has the reversed format, exit 0. */
-main () {
+int main (void) {
   /* This call has the arguments reversed.
      A reversed system may check and see that the address of main
      is not _IOLBF, _IONBF, or _IOFBF, and return nonzero.  */
@@ -1647,7 +1647,7 @@ LIBS="-lintl $LIBS"])])])
 AC_DEFUN(AC_FUNC_MEMCMP,
 [AC_CACHE_CHECK(for 8-bit clean memcmp, ac_cv_func_memcmp_clean,
 [AC_TRY_RUN([
-main()
+int main(void)
 {
   char c0 = 0x40, c1 = 0x80, c2 = 0x81;
   exit(memcmp(&c0, &c2, 1) < 0 && memcmp(&c1, &c2, 1) < 0 ? 0 : 1);
@@ -1805,7 +1805,7 @@ AC_TRY_RUN(
 #if !defined(__STDC__) || __STDC__ != 1
 #define volatile
 #endif
-main() {
+int main(void) {
   volatile char c = 255; exit(c < 0);
 }], ac_cv_c_char_unsigned=yes, ac_cv_c_char_unsigned=no)
 fi])
@@ -1819,7 +1819,7 @@ AC_DEFUN(AC_C_LONG_DOUBLE,
 [if test "$GCC" = yes; then
   ac_cv_c_long_double=yes
 else
-AC_TRY_RUN([int main() {
+AC_TRY_RUN([int main(void) {
 /* The Stardent Vistra knows sizeof(long double), but does not support it.  */
 long double foo = 0.0;
 /* On Ultrix 4.3 cc, long double is 4 and double is 8.  */
@@ -1834,7 +1834,7 @@ fi
 AC_DEFUN(AC_INT_16_BITS,
 [AC_OBSOLETE([$0], [; instead use AC_CHECK_SIZEOF(int)])dnl
 AC_MSG_CHECKING(whether int is 16 bits)
-AC_TRY_RUN([main() { exit(sizeof(int) != 2); }],
+AC_TRY_RUN([int main(void) { exit(sizeof(int) != 2); }],
  [AC_MSG_RESULT(yes)
  AC_DEFINE(INT_16_BITS)], AC_MSG_RESULT(no))
 ])
@@ -1842,7 +1842,7 @@ AC_TRY_RUN([main() { exit(sizeof(int) != 2); }],
 AC_DEFUN(AC_LONG_64_BITS,
 [AC_OBSOLETE([$0], [; instead use AC_CHECK_SIZEOF(long)])dnl
 AC_MSG_CHECKING(whether long int is 64 bits)
-AC_TRY_RUN([main() { exit(sizeof(long int) != 8); }],
+AC_TRY_RUN([int main(void) { exit(sizeof(long int) != 8); }],
  [AC_MSG_RESULT(yes)
  AC_DEFINE(LONG_64_BITS)], AC_MSG_RESULT(no))
 ])
@@ -1862,7 +1862,7 @@ AC_TRY_COMPILE([#include <sys/types.h>
  not big endian
 #endif], ac_cv_c_bigendian=yes, ac_cv_c_bigendian=no)])
 if test $ac_cv_c_bigendian = unknown; then
-AC_TRY_RUN([main () {
+AC_TRY_RUN([int main (void) {
   /* Are we little or big endian?  From Harbison&Steele.  */
   union
   {
@@ -1885,7 +1885,7 @@ AC_DEFUN(AC_C_INLINE,
 [AC_CACHE_CHECK([for inline], ac_cv_c_inline,
 [ac_cv_c_inline=no
 for ac_kw in inline __inline__ __inline; do
-  AC_TRY_COMPILE(, [} $ac_kw foo() {], [ac_cv_c_inline=$ac_kw; break])
+  AC_TRY_COMPILE(, [} $ac_kw foo(void) {], [ac_cv_c_inline=$ac_kw; break])
 done
 ])
 case "$ac_cv_c_inline" in
@@ -2277,7 +2277,7 @@ AC_DEFUN(AC_SYS_RESTARTABLE_SYSCALLS,
 #include <sys/types.h>
 #include <signal.h>
 ucatch (isig) { }
-main () {
+int main (void) {
   int i = fork (), status;
   if (i == 0) { sleep (3); kill (getppid (), SIGINT); sleep (3); exit (0); }
   signal (SIGINT, ucatch);
@@ -2654,7 +2654,7 @@ AC_CACHE_VAL(ac_cv_exeext,
   ac_cv_exeext=.exe
 else
   rm -f conftest*
-  echo 'int main () { return 0; }' > conftest.$ac_ext
+  echo 'int main (void) { return 0; }' > conftest.$ac_ext
   ac_cv_exeext=
   if AC_TRY_EVAL(ac_link); then
     for file in conftest.*; do