Memeory sanitizer compatibility are already done in MemorySanitizer::doInitialization. It verifies whether the necessary offsets exist and bails out if not. For this reason it is no good to duplicate two checks in two projects. This patch removes clang check and postpones msan compatibility validation till MemorySanitizer::doInitialization.
Another reason for this patch is to allow using msan with any CPU (given compatible runtime) and custom mapping provided via the arguments added by https://reviews.llvm.org/D44926.