* environ.cc: Eliminate oldstack CYGWIN option.

* exceptions.cc (sfta): Eliminate obsolete function.
(sgmb): Eliminate obsolete function.
(class stack_info): Remove MS method for walking the stack.
(stack_info::init): Just initialize required fields.
(stack_info::brute_force): Rename to stack_info::walk.
(handle_exceptions): Pass derived frame pointer to sig_send.
(interrupt_setup): Clear saved frame pointer here.
(interrupt_on_return): thestack is no longer a pointer.
(call_handler): Accept a flag to indicate when a signal was sent from other
than the main thread.  Use saved frame pointer for determining where to place
signal handler call.
(sig_handle): Accept "nonmain" argument.  Pass it to call_handler.
* fhandler_tty.cc (fhandler_tty_common::__acquire_output_mutex): Change
debugging output slightly.
* (fhandler_tty_common::__release_output_mutex): Ditto.
(fhandler_tty_slave::read): Fix a comment, remove a goto.
* sigproc.cc (sig_send): Accept an optional frame pointer argument for use when
suspending the main process.  sigcomplete_main is an autoreset event now.  Save
frame pointer for non-main operation.
(wait_sig): Make sigcomplete_main an autoreset event.  Eliminate NOSIGQUEUE.
Pass rc to sig_handle to signify if this was a nonmain process.
* sigproc.h: Reflect change to sig_send argument.
* syscalls.cc (swab): Eliminate swab function since it is now available in
newlib.
* winsup.h (signal_dispatch): Change CONTEXT cx to DWORD ebp.

winsup/cygwin/winsup.h

@@ -307,7 +307,7 @@ struct signal_dispatch
   void (*func) (int);
   int sig;
   int saved_errno;
-  CONTEXT *cx;
+  DWORD ebp;
   DWORD oldmask;
   DWORD retaddr;
 };