Avoid an implicit declaration of the malloc function.  Improves C99

compatibility.

Submitted upstream:

  <https://lists.gnu.org/archive/html/emacs-devel/2022-12/msg01020.html>

diff --git a/configure.ac b/configure.ac

index cc390d40b33a1d8f..7be08de740cfc486 100644

--- a/configure.ac

+++ b/configure.ac

@@ -4590,6 +4590,7 @@ AC_CACHE_CHECK([whether signals can be handled on alternate stack],

 	       [emacs_cv_alternate_stack],

   [AC_COMPILE_IFELSE(

      [AC_LANG_PROGRAM([[#include <signal.h>

+			#include <stdlib.h>

 		      ]],

 		      [[stack_t ss;

 			struct sigaction sa;