Fix generic C99 compatibility issue in the configure script because it
was generated by a historic autoconf version.  This will go away once
upstream re-runs autoconf, and until then, the patch will keep
applying, so there is no need to upstream it.

diff --git a/src/lt/configure b/src/lt/configure
index e3f5aa6ed9a21307..aa4f50637331d427 100755
--- a/src/lt/configure
+++ b/src/lt/configure
@@ -2465,7 +2465,7 @@ if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
   echo "$as_me:$LINENO: \$? = $ac_status" >&5
   (exit $ac_status); }; }; then
   for ac_declaration in \
-   '' \
+   '#include <stdlib.h>' \
    'extern "C" void std::exit (int) throw (); using std::exit;' \
    'extern "C" void std::exit (int); using std::exit;' \
    'extern "C" void exit (int) throw ();' \
@@ -3640,8 +3640,8 @@ main ()
   for (i = 0; i < 256; i++)
     if (XOR (islower (i), ISLOWER (i))
 	|| toupper (i) != TOUPPER (i))
-      exit(2);
-  exit (0);
+      return 2;
+  return 0;
 }
 _ACEOF
 rm -f conftest$ac_exeext