Add error checking to mutexes and condition variables.

Add error checking to mutexes and condition variables.

After the discussions about PTHREAD_PROCESS_SHARED and after
observing that on Cygwin the program simply hangs because
this flag is not implemented there, the best way is to check
for errors and exit with a clear error message instead of
some mysterious hang.

libgfortran/ChangeLog:

	* caf_shared/util.c (ERRCHECK): New macro.
	(initialize_shared_mutex): Use it to check return codes.
	(initialize_shared_condition): Likewise.