AIX libstdc++ breakage after libgcc changes

[David Edelsohn]

Rainer and I greatly would appreciate some libstdc++ help debugging
the AIX failure after the libgcc and gthr changes.  Please see PR
50982.

The changes to gthr have caused differences when compiling atomic.cc,
leading to a C++ error referring to pthread_once_t.

rev 180770 is before the libgcc/gthr patch and rev 180821 is after the patch.

The change causes a difference in macros from autoconf, leading to
other code differences.  the culprit seems to be related to
_GLIBCXX_HAS_GTHREADS newly defined after the change affecting
libstdc++ header file "mutex".  It's not clear why this was not
defined before and may have exposed a latent bug.

diff -u atomic.ii.save-temps.old atomic.ii.save-temps.new

-#define __VERSION__ "4.7.0 20111102 (experimental) [trunk revision 180770]"
+#define __VERSION__ "4.7.0 20111103 (experimental) [trunk revision 180821]"

-
-#define _GLIBCXX_HAVE_GTHR_DEFAULT 1
-
-

-
+#define _GLIBCXX_HAS_GTHREADS 1

Thanks, David