[patch] fix spurious SIGSEGV faults under Cygwin

[Brian Dessent]

Dave Korn wrote:

>   I'm having a conceptual difficulty here: Under what circumstances would you expect there *not* to be a debugger attached to the
> inferior to which the debugger is attached?  That's a bit zen, isn't it?

The code in question here runs many times in the normal course of any
Cygwin program -- debugger or no.  The idea behind guarding the call to
OutputDebugString() with "if (being_debugged())" was that the call to
IsDebuggerPresent() was cheaper than the call to OutputDebugString(),
and that a well-behaived, non-debug build of a binary should not
needlessly send tons and tons of nonsense to OutputDebugString unless
it's actually being debugged and there is something there to interpret
the nonsense.

Brian