[Cygwin] Fix for: detaching crashes the inferior.

[Pedro Alves]

Hi all,

Detaching on Cygwin often crashes the inferior, either
when gdb attaches to the inferior, or when gdb launches
the inferior as a child.

Initially I thought that somehow the FLAGS_TRACE_BIT
would be set in the context, and after detaching there would
be no debugger to catch the exception, but it turns out that
it isn't the case - I couldn't find a case where FLAGS_TRACE_BIT
was set.  But, surprisingly doing a SetThreadContext with
CONTEXT_CONTROL makes the crashes go away - even if you don't
change the contents of the context.  I'm not 100% sure why, but,
it fixes it.  If MSFT sends me the Windows sources, I'll look
deeper :)

No regressions on i686-pc-cygwin on XP Pro.

OK?

Cheers,
Pedro Alves




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