WIP: Enable using memory sanitizer with Julia

Memory sanitizer is a Valgrind like tool, but about 10x faster and uses compiler techniques rather than dynamic execution. You'll need this patch to LLVM https://gist.github.com/Keno/8748036. I basically put this here in case anyone wants to play with it, because I might not get to it in a while. 

[pao: update gist link]
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