https://github.com/vim/vim/pull/11496

From 360b569f86b851c37e32b7cfaec079823188ff27 Mon Sep 17 00:00:00 2001
From: Sam James <sam@gentoo.org>
Date: Fri, 4 Nov 2022 03:18:23 +0000
Subject: [PATCH] configure.ac: Fix -Wimplicit-int

Clang 16 makes -Wimplicit-int an error by default. Fixes errors like:
```
error: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Werror,-Wimplicit-int]
```

We already use proper declarations with every other test anyway, so
let's be consistent.

Signed-off-by: Sam James <sam@gentoo.org>
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -3654,7 +3654,7 @@ dnl check if struct sigcontext is defined (used for SGI only)
 AC_MSG_CHECKING(for struct sigcontext)
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([
 #include <signal.h>
-test_sig()
+int test_sig()
 {
     struct sigcontext *scont;
     scont = (struct sigcontext *)0;