gdbstub initial code, v15

[Oleg Nesterov <oleg at redhat dot com>]

I just realized I forgot to send V15 before (I was distracted by
sigaltack bugreport).

Changes: multiple watchpoints.

	> Any advice is very much appreciated. Most probably, there is no any
	> clever solution. Once a traced sub-thread detects that a watchpoint
	> was changed, it should mark this wp as "reported" for other threads
	> and report it to gdb. IOW, we report the random thread and random wp.

This is what ugdb does. I don't think we can do something better
without changing the remote protocol.

Unfinished: support "signal SIG" in T00 case correctly (without
another report to gdb).

Next: hardware watchpoints. But this is tricky, and right now I am
not sure ugdb can do this (at least unless we ignore conflicts with
other users of debugregX/ptrace_bps).

Oleg.

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