Based on a Debian patch:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=829327

--- lame-3.100/configure.in
+++ lame-3.100/configure.in
@@ -1240,6 +1240,7 @@
 
 AC_CONFIG_FILES([Makefile \
 		 libmp3lame/Makefile \
+		 libmp3lame/lame.pc \
 		 libmp3lame/i386/Makefile \
 		 libmp3lame/vector/Makefile \
 		 frontend/Makefile \
--- lame-3.100/libmp3lame/Makefile.am
+++ lame-3.100/libmp3lame/Makefile.am
@@ -31,6 +31,7 @@
 
 EXTRA_DIST = \
 	lame.rc \
+	lame.pc.in \
 	vbrquantize.h \
 	logoe.ico
 
@@ -100,3 +101,8 @@
 #$(OBJECTS): libtool
 #libtool: $(LIBTOOL_DEPS)
 #	$(SHELL) $(top_builddir)/config.status --recheck
+
+pkgconfigdir = $(libdir)/pkgconfig
+pkgconfig_DATA = lame.pc
+
+DISTCLEANFILES = $(pkgconfig_DATA)
--- lame-3.100/libmp3lame/lame.pc.in
+++ lame-3.100/libmp3lame/lame.pc.in
@@ -0,0 +1,10 @@
+prefix=@prefix@
+exec_prefix=@exec_prefix@
+libdir=@libdir@
+includedir=@includedir@
+
+Name: @PACKAGE_NAME@
+Description: MP3 encoding library
+Version: @PACKAGE_VERSION@
+Libs: -L${libdir} -lmp3lame
+Cflags: -I${includedir}/lame