https://github.com/SawfishWM/librep/pull/17

From 5c653297288fc1d82f92d224c745d89f9e6734fd Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Sat, 5 Nov 2022 06:04:27 +0000
Subject: [PATCH] build: fix -Wimplicit-int, -Wimplicit-function-declaration

Clang 16 will make -Wimplicit-int and -Wimplicit-function-declaration
errors by default.

In this case, it manifests as:
```
checking for data type to store Lisp values... configure: error: cannot find Lisp value type; set --with-value-type (see README)
```

For more information, see LWN.net [0] or LLVM's Discourse [1], or the
(new) c-std-porting mailing list [2].

[0] https://lwn.net/Articles/913505/
[1] https://discourse.llvm.org/t/configure-script-breakage-with-the-new-werror-implicit-function-declaration/65213
[2] hosted at lists.linux.dev.

Signed-off-by: Sam James <sam@gentoo.org>
--- a/configure.ac
+++ b/configure.ac
@@ -432,15 +432,18 @@ AC_ARG_WITH(value-type,
 			   as a pointer. [TYPE=<probed>] (see README)], [],
  [with_value_type="undef"])
 if test "${with_value_type}" = "undef"; then
-  AC_TRY_RUN([main () { exit (!(sizeof (int) >= sizeof (void *)));}],
+  AC_TRY_RUN([#include <stdlib.h>
+             int main () { exit (!(sizeof (int) >= sizeof (void *)));}],
 	     [with_value_type=int])
 fi
 if test "${with_value_type}" = "undef"; then
-  AC_TRY_RUN([main () { exit (!(sizeof (long int) >= sizeof (void *)));}],
+  AC_TRY_RUN([#include <stdlib.h>
+             int main () { exit (!(sizeof (long int) >= sizeof (void *)));}],
 	     [with_value_type="long int"])
 fi
 if test "${with_value_type}" = "undef"; then
-  AC_TRY_RUN([main () { exit (!(sizeof (long long int) >= sizeof (void *)));}],
+  AC_TRY_RUN([#include <stdlib.h>
+             int main () { exit (!(sizeof (long long int) >= sizeof (void *)));}],
 	     [with_value_type="long long int"])
 fi
 if test "${with_value_type}" = "undef"; then
@@ -457,7 +460,8 @@ AC_ARG_WITH(value-sizeof,
 if test "${with_value_sizeof}" = "undef"; then
   dnl the following fragment is inspired by AC_CHECK_SIZEOF
   AC_TRY_RUN([#include <stdio.h>
-	      main () {
+		#include <stdlib.h>
+		int main () {
 		FILE *f = fopen ("conftestval", "w");
 		if (!f) exit (1);
 		fprintf (f, "%d\n", sizeof (${with_value_type}));
@@ -548,11 +552,12 @@ if test "${with_stack_direction}" = unknown; then
   esac
 fi
 if test "${with_stack_direction}" = unknown; then
-  AC_TRY_RUN([ int level = 1;
-	       void inner (char *foo) { char bar;
+  AC_TRY_RUN([#include <stdlib.h>
+		 int level = 1;
+		 void inner (char *foo) { char bar;
 		 if (level) { --level; inner (foo); }
 		 exit (!(foo >= &bar)); }
-	       void main () { char foo; inner (&foo); } ],
+	       int main () { char foo; inner (&foo); } ],
    [AC_MSG_RESULT([downwards])
     with_stack_direction=-1],
    [AC_MSG_RESULT([upwards])