[config] Added #define for __USE_GNU when building Parrot with GNU libc backtrace() support.  I'm not completely convinced this will work on Mac OS X, but we can refine it further if necessary.  See RT #58670, reported by Christoph Otto.
[config] Added #define for __USE_GNU when building Parrot with GNU libc
backtrace() support.  I'm not completely convinced this will work on Mac OS X,
but we can refine it further if necessary.  See RT #58670, reported by
Christoph Otto.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@33502 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

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