Alas, roll back the definition of _XOPEN_SOURCE. It breaks the tests

for the time module, because somehow configure won't define the
symbols HAVE_STRUCT_TM_TM_ZONE, HAVE_TM_ZONE, and HAVE_TZNAME in this
case.

I've got no time to research this further, so I leave it in Jeremy and
Martin's capable hands to find a different solution for True64 (or to
devise a way to get the time tests to succeed while defining
_XOPEN_SOURCE).

configure

@@ -1,5 +1,5 @@
 #! /bin/sh
-# From configure.in Revision: 1.332 .
+# From configure.in Revision: 1.333 .
 # Guess values for system-dependent variables and create Makefiles.
 # Generated by GNU Autoconf 2.53.
 #
@@ -1225,12 +1225,6 @@ VERSION=2.3
 
 SOVERSION=1.0
 
-
-cat >>confdefs.h <<\_ACEOF
-#define _XOPEN_SOURCE 500
-_ACEOF
-
-
 # Arguments passed to configure.
 
 CONFIG_ARGS="$ac_configure_args"

configure.in

@@ -20,8 +20,6 @@ VERSION=2.3
 AC_SUBST(SOVERSION)
 SOVERSION=1.0
 
-AC_DEFINE(_XOPEN_SOURCE, 500, [Needed on Tru64 and does no harm on Linux])
-
 # Arguments passed to configure.
 AC_SUBST(CONFIG_ARGS)
 CONFIG_ARGS="$ac_configure_args"

pyconfig.h.in

@@ -773,9 +773,6 @@
 /* Define to force use of thread-safe errno, h_errno, and other functions */
 #undef _REENTRANT
 
-/* Needed on Tru64 and does no harm on Linux */
-#undef _XOPEN_SOURCE
-
 /* Define to 1 if type `char' is unsigned and you are not using gcc.  */
 #ifndef __CHAR_UNSIGNED__
 # undef __CHAR_UNSIGNED__