Use -D_GLIBCXX_DEBUG

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

Ooh cool. I'd strongly prefer that we fix the bugs in LLVM before enabling this :slight_smile:

-Chris

Ok, I'll coordinate with Dan and Jeff and get our fixes back before I
submit a change to enable this for debug builds.

                                                -Dave