Fix implicit function declarations in configure.ac (XOpenDisplay, malloc)
Backported from master branch
https://bugs.gentoo.org/898304

commit 6c1413d5ef0d1fea639b0d8c83a0c0065d99359b
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Dec 23 18:49:25 2022 +0100

    configure: Remove obsolete check for -b i486-linuxaout

commit 121a9ff9f6fc69066ce30c2dbe6cbfbfdca6aeaa
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Dec 23 18:51:08 2022 +0100

    Fix alternate stack test in configure

--- emacs-28.2/configure.ac
+++ emacs-28.2/configure.ac
@@ -2491,39 +2491,6 @@
     export LD_RUN_PATH
   fi
 
-  if test "${opsys}" = "gnu-linux"; then
-    AC_CACHE_CHECK([whether X on GNU/Linux needs -b to link], [emacs_cv_b_link],
-    [AC_LINK_IFELSE([AC_LANG_PROGRAM([[]],
-     [[XOpenDisplay ("foo");]])],
-     [xgnu_linux_first_failure=no],
-     [xgnu_linux_first_failure=yes])
-    if test "${xgnu_linux_first_failure}" = "yes"; then
-      OLD_CPPFLAGS="$CPPFLAGS"
-      OLD_LIBS="$LIBS"
-      CPPFLAGS="$CPPFLAGS -b i486-linuxaout"
-      LIBS="$LIBS -b i486-linuxaout"
-      AC_LINK_IFELSE([AC_LANG_PROGRAM([[]],
-       [[XOpenDisplay ("foo");]])],
-       [xgnu_linux_second_failure=no],
-       [xgnu_linux_second_failure=yes])
-      if test "${xgnu_linux_second_failure}" = "yes"; then
-	# If we get the same failure with -b, there is no use adding -b.
-	# So leave it out.  This plays safe.
-        emacs_cv_b_link=no
-      else
-        emacs_cv_b_link=yes
-      fi
-      CPPFLAGS=$OLD_CPPFLAGS
-      LIBS=$OLD_LIBS
-    else
-      emacs_cv_b_link=no
-    fi])
-    if test "x$emacs_cv_b_link" = xyes ; then
-      LD_SWITCH_X_SITE="$LD_SWITCH_X_SITE -b i486-linuxaout"
-      C_SWITCH_X_SITE="$C_SWITCH_X_SITE -b i486-linuxaout"
-    fi
-  fi
-
   # Reportedly, some broken Solaris systems have XKBlib.h but are missing
   # header files included from there.
   AC_CACHE_CHECK([for Xkb], [emacs_cv_xkb],
@@ -4629,6 +4596,7 @@
 	       [emacs_cv_alternate_stack],
   [AC_COMPILE_IFELSE(
      [AC_LANG_PROGRAM([[#include <signal.h>
+			#include <stdlib.h>
 		      ]],
 		      [[stack_t ss;
 			struct sigaction sa;