Avoid implicit function declarations.  The change around ac_declaration
always includes <stdlib.h> for the exit prototype.  For
ac_cv_header_stdc, use return from main instead of exit.

configure.in is not updated because these faulty checks are generated
by an old version of autoconf.

diff --git a/configure b/configure
index bede66c41e9412ec..45bd0df4a4cc2b00 100755
--- a/configure
+++ b/configure
@@ -2786,7 +2786,7 @@ if { (eval echo "$as_me:$LINENO: \"$ac_compile\"") >&5
   echo "$as_me:$LINENO: \$? = $ac_status" >&5
   (exit $ac_status); }; }; then
   for ac_declaration in \
-   '' \
+   '#include <stdlib.h>' \
    'extern "C" void std::exit (int) throw (); using std::exit;' \
    'extern "C" void std::exit (int); using std::exit;' \
    'extern "C" void exit (int) throw ();' \
@@ -4323,8 +4323,8 @@ main ()
   for (i = 0; i < 256; i++)
     if (XOR (islower (i), ISLOWER (i))
 	|| toupper (i) != TOUPPER (i))
-      exit(2);
-  exit (0);
+      return 2;
+  return 0;
 }
 _ACEOF
 rm -f conftest$ac_exeext
@@ -4827,7 +4827,7 @@ else
   fi
 fi
 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 ();' \
@@ -18961,7 +18961,7 @@ else
   fi
 fi
 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 ();' \
diff --git a/perl/configure b/perl/configure
index cdf6f468270ec687..ba2721b9c04a9931 100755
--- a/perl/configure
+++ b/perl/configure
@@ -1562,7 +1562,6 @@ if { (eval echo "$as_me:1553: \"$ac_compile\"") >&5
   echo "$as_me:1562: \$? = $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;' \