Fix compilation with -fno-common (default for GCC 10)

Signed-off-by: Marek Behún kabel@blackhole.sk>
---
diff --git a/lib/sstrlib/sstr_private.h b/lib/sstrlib/sstr_private.h
--- a/lib/sstrlib/sstr_private.h
+++ b/lib/sstrlib/sstr_private.h
@@ -32,6 +32,6 @@ struct _sstr {
 };
 
 int sstr_alloc_space(sstr * p, int len);
-void (*on_error) (void);
+extern void (*on_error) (void);
 
 #endif /*SSTR_PRIVATE_H */
diff --git a/src/common.h b/src/common.h
--- a/src/common.h
+++ b/src/common.h
@@ -184,7 +184,7 @@ typedef struct _session_info {
 /*******************
 **Global Variables**
 ********************/
-session_info *info;
+extern session_info *info;
 extern pid_t cmgrpid, tdatapid;
 
 #endif /* COMMON_H */
diff --git a/src/ftp-cmds.c b/src/ftp-cmds.c
--- a/src/ftp-cmds.c
+++ b/src/ftp-cmds.c
@@ -38,6 +38,8 @@ void xfer_command(sstr * cmd, sstr * arg
 void cwd_command(sstr * cmd, sstr * arg);
 void pasv_reply(sstr * msg);
 
+struct cmd_struct *ftp_cmds;
+
 void ftpcmds_init()
 {
 	static struct cmd_struct list[] = {	/*Pinched in part SUSE */
diff --git a/src/ftp-cmds.h b/src/ftp-cmds.h
--- a/src/ftp-cmds.h
+++ b/src/ftp-cmds.h
@@ -33,7 +33,7 @@ struct cmd_struct {
 	void (*cmd) (sstr * cmd, sstr * arg);
 };
 
-struct cmd_struct *ftp_cmds;
+extern struct cmd_struct *ftp_cmds;
 void user_munge(sstr * cmd, sstr * arg);
 
 
diff --git a/src/main.c b/src/main.c
--- a/src/main.c
+++ b/src/main.c
@@ -62,6 +62,8 @@ static struct client_info {
 void add_client(pid_t, struct sockaddr_in client);
 void rm_client(pid_t pid);
 
+session_info *info;
+
 #ifdef ENABLE_CHANGEPROC
 int main(int argc, char *argv[], char *envp[])
 #else