[LLVMdev] Use -D_GLIBCXX_DEBUG

[David A. Greene]

I just made a patch to our local llvm build here to pass -D_GLIBCXX_DEBUG when
building llvm.  This switch turns on debug code in libstdc++ that checks for
various violations.  We've already discovered several llvm bugs with it.  
Should I commit a change back to the official sources?  It will almost 
certainly cause tests to fail, but that's a GOOD thing.

                                                      -Dave