* spawn.cc (pthread_cleanup::oldmask): Default to invalid signal mask.

(do_cleanup): Test for invalid signal mask to decide whether to restore the
mask rather than assuming zero mask indicates that there is nothing to do.

winsup/cygwin/cygheap.h

@@ -278,6 +278,7 @@ struct init_cygheap
   size_t sthreads;
   int open_fhs;
   pid_t pid;			/* my pid */
+  const char *system_root;
   void close_ctty ();
 };