Fix compilation with clang-16

aclocal.m4 contains code that no longer compiles: missing headers and missing
return types.

--- a/autoconf_local/aclocal.m4
+++ b/autoconf_local/aclocal.m4
@@ -192,6 +192,7 @@
 #include "pchtest.h"
 #pragma hdrstop
 #include <stdarg.h>
+#include <stdlib.h>
 
 int main(int argc, char **argv)
 {
@@ -1242,7 +1243,9 @@
 AC_MSG_CHECKING([if -D__STDC_EXT__ is needed with GCC on HP-UX])
 AC_TRY_RUN([
 #include <stdio.h>
+#include <stdlib.h>
  
+int
 main()
 {
 #ifdef __STDC_EXT__
@@ -1674,7 +1677,9 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <stdio.h>
+#include <stdlib.h>
  
+int
 main()
 {
 	int result;
@@ -1816,6 +1821,7 @@
 #	include <snprintf.h>
 #endif
  
+int
 main()
 {
 	char s[16];
@@ -1876,6 +1882,7 @@
 #	include <snprintf.h>
 #endif
  
+int
 main()
 {
 	int result;
@@ -2004,7 +2011,9 @@
 #ifdef HAVE_SYS_UN_H
 #include <sys/un.h>
 #endif
+#include <stdlib.h>
  
+int
 main()
 {
 	int sfd;
@@ -2088,7 +2097,9 @@
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <netdb.h>
+#include <stdlib.h>
  
+int
 main()
 {
 	struct hostent *hp1, *hp2;
@@ -2134,6 +2145,7 @@
 #endif
 #include <sys/types.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 /* These are needed if libwrap.a was compiled with
  * PROCESS_OPTIONS defined.
@@ -2238,6 +2250,7 @@
 #include <stdio.h>
 #include <signal.h>
 #include <setjmp.h>
+#include <stdlib.h>
 ],[
 	/* function-body */
 	sigjmp_buf sjb;
@@ -2265,6 +2278,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmp.h>
+#include <stdlib.h>
 ],[
 struct utmp u;
 
@@ -2288,6 +2302,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmp.h>
+#include <stdlib.h>
 ],[
 struct utmp u;
 
@@ -2311,6 +2326,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmpx.h>
+#include <stdlib.h>
 ],[
 struct utmpx u;
 
@@ -2334,6 +2350,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmpx.h>
+#include <stdlib.h>
 ],[
 struct utmpx u;
 
@@ -2357,6 +2374,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmpx.h>
+#include <stdlib.h>
 ],[
 struct utmpx u;
 
@@ -2380,6 +2398,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmp.h>
+#include <stdlib.h>
 ],[
 struct utmp u;
 
@@ -2403,6 +2422,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmp.h>
+#include <stdlib.h>
 ],[
 struct utmp u;
 
@@ -2427,6 +2447,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmp.h>
+#include <stdlib.h>
 ],[
 struct utmp u;
 
@@ -2450,6 +2471,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <utmp.h>
+#include <stdlib.h>
 ],[
 struct utmp u;
 
@@ -2482,6 +2504,7 @@
 #include <stdio.h>
 #include <stdlib.h>
  
+int
 main()
 {
 	size_t x = 0;
@@ -2545,6 +2568,7 @@
 #include <stdio.h>
 #include <stdlib.h>
  
+int
 main()
 {
 	off_t x = 0;
@@ -2608,6 +2632,7 @@
 #include <stdio.h>
 #include <stdlib.h>
  
+int
 main()
 {
 	struct stat x;
@@ -2671,6 +2696,7 @@
 #include <stdio.h>
 #include <stdlib.h>
  
+int
 main()
 {
 	off64_t x = 0;
@@ -2732,6 +2758,7 @@
 #include <stdio.h>
 #include <stdlib.h>
  
+int
 main()
 {
 	struct stat64 x;
@@ -2789,6 +2816,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <stdlib.h>
 ],[
 struct stat64 st;
 
@@ -2815,6 +2843,7 @@
 #include <sys/uio.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#include <stdlib.h>
 ],[
 struct cmsghdr cm;
 
@@ -2844,6 +2873,7 @@
 #include <sys/uio.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#include <stdlib.h>
 ],[
 struct msghdr m;
 
@@ -2872,6 +2902,7 @@
 #include <sys/uio.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#include <stdlib.h>
 ],[
 struct msghdr m;
 
@@ -2975,6 +3006,8 @@
 #include <sys/uio.h>
 #include <sys/socket.h>
 #include <sys/un.h>
+#include <stdlib.h>
+#include <string.h>
 ],[
 struct sockaddr_un uaddr;
 
@@ -3004,6 +3037,7 @@
 #elif defined(HAVE_SYS_VFS_H)
 #	include <sys/vfs.h>
 #endif
+#include <stdlib.h>
 ],[
 struct statfs st;
 
@@ -3027,6 +3061,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/statvfs.h>
+#include <stdlib.h>
 ],[
 struct statvfs st;
 
@@ -3049,7 +3084,9 @@
 	/* program */
 #include <stdio.h>
 #include <string.h>
+#include <stdlib.h>
  
+int
 main()
 {
 	int result;
@@ -3108,9 +3145,11 @@
 #endif
 #include <stdio.h>
 #include <string.h>
+#include <stdlib.h>
 
 extern char *crypt(const char *key, const char *salt);
 
+int
 main()
 {
 	char cleartext[256];
@@ -3182,6 +3221,7 @@
 #include <sys/socket.h>
 #include <arpa/inet.h>
 #include <netinet/in.h>
+#include <string.h>
 #ifdef HAVE_ARPA_NAMESER_H
 #	include <arpa/nameser.h>
 #endif
@@ -3327,9 +3367,11 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 extern char *rl_library_version;
 
+int
 main()
 {
 	FILE *fp;
@@ -3446,9 +3488,11 @@
 #endif
 #include <sys/types.h>
 #include <stdio.h>
+#include <stdlib.h>
 
 long long hugeNumvar = 1;
 
+int
 main()
 {
 	long long hugeNumtoo = 2;
@@ -3495,6 +3539,7 @@
 #include <string.h>
 #include <stdlib.h>
 
+int
 main()
 {
 	char s[80];
@@ -3536,6 +3581,7 @@
 #include <string.h>
 #include <stdlib.h>
 
+int
 main()
 {
 	char s[80];
@@ -3585,6 +3631,7 @@
 #include <string.h>
 #include <stdlib.h>
 
+int
 main()
 {
 	long long hugeNum, justAsHugeNum;
@@ -3629,6 +3676,7 @@
 #include <string.h>
 #include <stdlib.h>
 
+int
 main()
 {
 	long long hugeNum, justAsHugeNum;
@@ -4076,7 +4124,7 @@
 #include <sys/select.h>
 #endif
 #include <sys/socket.h>	/* MG: always incl */
-extern select ($ac_cv_func_select_arg1,$ac_cv_func_select_arg234,$ac_cv_func_select_arg234,$ac_cv_func_select_arg234,$ac_cv_func_select_arg5);],,dnl
+extern int select ($ac_cv_func_select_arg1,$ac_cv_func_select_arg234,$ac_cv_func_select_arg234,$ac_cv_func_select_arg234,$ac_cv_func_select_arg5);],,dnl
         [ac_not_found=no ; break 3],ac_not_found=yes)
       done
      done
@@ -4226,7 +4274,9 @@
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <netdb.h>
+#include <stdlib.h>
 
+int
 main()
 {
 	exit(0);
@@ -5023,6 +5073,7 @@
 		/* includes */
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 
 #ifdef HAVE_NCURSES_H
 #	define NCURSES_OPAQUE 0
@@ -5054,6 +5105,7 @@
 #endif
 
  
+int
 main(int argc, char **argv)
 {
 	/* Note:  don't actually call curses, since it may block;
@@ -5142,6 +5194,7 @@
 #	include <curses.h>
 #endif
 
+int
 main()
 {
 	exit(0);
@@ -5809,7 +5862,9 @@
 		cat <<EOF > "$vertest.c"
 #include <stdio.h>
 #include <gnu/libc-version.h>
+#include <stdlib.h>
 
+int
 main()
 {
 	const char *ver = gnu_get_libc_version();
@@ -5957,6 +6012,7 @@
 #include <stdlib.h>
 #include <ctype.h>
 
+int
 main()
 {
 	char line[256], *cp, *cp2; 
@@ -6109,6 +6165,7 @@
 #include <stdio.h>
 #include <stdlib.h>
  
+int
 main()
 {
 	FILE *fp;
@@ -6166,6 +6223,7 @@
 #include <stdio.h>
 #include <stdlib.h>
  
+int
 main()
 {
 	struct stat x;
@@ -6224,6 +6282,7 @@
 #include <stdio.h>
 #include <stdlib.h>
  
+int
 main()
 {
 	struct stat64 x;
@@ -6457,7 +6516,8 @@
 	  ac_cv_func_setvbuf_reversed,
 	[AC_TRY_RUN([#include <stdio.h>
 	/* If setvbuf has the reversed format, exit 0. */
-	main () {
+	#include <stdlib.h>
+	int main () {
 	  /* 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.  */