aclocal.m4 contains missing headers

https://bugs.gentoo.org/875458
https://bugs.gentoo.org/921487
https://bugs.gentoo.org/926491

--- a/autoconf_local/aclocal.m4
+++ b/autoconf_local/aclocal.m4
@@ -3341,7 +3341,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 		 
-			main(int argc, char **argv)
+			int main(int argc, char **argv)
 			{
 				/* Note:  don't actually call readline,
 				 * since it may block;
@@ -5107,6 +5107,7 @@
 		/* includes */
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #ifdef HAVE_NCURSES_H
 #	define NCURSES_OPAQUE 0
@@ -5139,7 +5139,7 @@
 #endif
 
  
-main(int argc, char **argv)
+int main(int argc, char **argv)
 {
 	/* Note:  don't actually call curses, since it may block;
 	 * We just want to see if it (dynamic) linked in okay.
@@ -6531,6 +6531,7 @@
 	AC_CACHE_CHECK(whether setvbuf arguments are reversed,
 	  ac_cv_func_setvbuf_reversed,
 	[AC_TRY_RUN([#include <stdio.h>
+	#include <stdlib.h>
 	/* If setvbuf has the reversed format, exit 0. */
 	main () {
 	  /* This call has the arguments reversed.