* sigproc.cc (wait_sig): Remove unneeded for loop iteration.

* exceptions.cc (interrupt_setup): Don't set signal mask here or races occur
with main thread.  Set it in sigdelayed instead.
(sigreturn): Reflect change in stack order of ebp and flags.
(sigdelayed): Set stack frame correctly.  Call set_process_mask here with flags
for last trapped signal.
(signal_dispatch): Add newmask.
* sigproc.cc (wait_sig): Eliminate ill-considered attempt to halt looping
signal processors.

winsup/cygwin/perthread.h

@@ -97,6 +97,7 @@ struct signal_dispatch
   int sig;
   int saved_errno;
   DWORD oldmask;
+  DWORD newmask;
   DWORD retaddr;
   DWORD *retaddr_on_stack;
 };