Avoid calling an undeclared exit function, to increase compatibility
with stricter C99 compilers.  There is no need to upstream this
because this code is coming from autoconf, and the issue will go away
once the configure script is regenerated.

diff --git a/configure b/configure
index 8d07a39f42caec75..1eecdde151cc70e8 100755
--- a/configure
+++ b/configure
@@ -2104,7 +2104,7 @@ if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
   echo "$as_me:$LINENO: \$? = $ac_status" >&5
   (exit $ac_status); }; }; then
   for ac_declaration in \
-   '' \
+   '#include <stdlib.h>' \
    'extern "C" void std::exit (int) throw (); using std::exit;' \
    'extern "C" void std::exit (int); using std::exit;' \
    'extern "C" void exit (int) throw ();' \
@@ -2714,8 +2714,8 @@ main ()
   for (i = 0; i < 256; i++)
     if (XOR (islower (i), ISLOWER (i))
 	|| toupper (i) != TOUPPER (i))
-      exit(2);
-  exit (0);
+      return 2;
+  return 0;
 }
 _ACEOF
 rm -f conftest$ac_exeext