[Bug libstdc++/51906] thread lock test failures on darwin11 under Xcode 4.2

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51906

--- Comment #24 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-01-31 00:01:41 UTC ---
That debug session still doesn't make much sense, are you debugging an
optimised executable?   I don't need a more detailed trace, just one that
actually shows what happens!  e.g. knowing what pthread_mutex_trylock returns
is necessary, knowing the details of what happens inside that function isn't
necessary.


What does this return?

#include <pthread.h>

struct mutex {
   pthread_mutex_t m = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;
};

int main()
{
  mutex m;
  return pthread_mutex_trylock(&m.m);
}

If the solution is simply to define _XOPEN_SOURCE then that should be done for
Lion, but a relevant maintainer for that target should make that decision. 
libstdc++ relies on POSIX features so if they aren't correctly defined without
_XOPEN_SOURCE then that is needed (on GNU/Linux _GNU_SOURCE is always defined)