I believe this is already fixed upstream by https://reviews.llvm.org/D68313 but I guess our Clang won't have that fix yet?
Bug 1581584 Comment 14 Edit History
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Edit: Nevermind, I misread the question ;) Sure, I could do that if it applies cleanly. I'll leave the needinfo here since I need to finish some other stuff first but then I can look. We also used to have Clang Trunk builds that we could use for ASan instead if the patch can't be backported easily.