Fix C99 compatibility issues in the autoconf-generated code.  This

has already been fixed in autoconf, so there is no need to upstream

this change for sage.

diff --git a/configure b/configure

index b8060da2cecf8c49..4de2f86274c03abb 100755

--- a/configure

+++ b/configure

@@ -3000,7 +3000,7 @@ 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 ();' \

@@ -4509,8 +4509,8 @@ 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

@@ -19514,7 +19514,7 @@ 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 ();' \