Bug 837845 - Manually backout the largest memory users from bug 798624; r=Waldo a=lsblakk

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extra : rebase_source : 55e61500dac9d0ab84706ff688124c7b0a03fd66
Bug 830676 - YarrJIT is broken on Win64 after landing bug 820124. r=sstangl, a=lsblakk
Bug 834762 - yarr/MatchResult.h:58:44: warning: overflow in implicit constant conversion [-Woverflow].  r=warning-spam, a=lsblakk