Enable msan unconditionally on Linux

[vit9696]

Summary

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.

[eugenis]

I too find these checks arbitrary and pointless. @kcc ?

[vit9696]

Now that https://reviews.llvm.org/D44926 was merged upstream, may I request this to be merged as well?
As stated above it is pretty much pointless to have the check doubled, and after more than a week nobody thought of any issue.
Thanks :)

[eugenis]

Merged. Please don't forget to update tests next time.

lib/Driver/ToolChains/Linux.cpp

const bool IsArmArch = getTriple().getArch() == llvm::Triple::arm ||
                          getTriple().getArch() == llvm::Triple::thumb ||
                          getTriple().getArch() == llvm::Triple::armeb ||
                          getTriple().getArch() == llvm::Triple::thumbeb;
   SanitizerMask Res = ToolChain::getSupportedSanitizers();
   Res |= SanitizerKind::Address;
   Res |= SanitizerKind::Fuzzer;
   Res |= SanitizerKind::FuzzerNoLink;
   Res |= SanitizerKind::KernelAddress;
+  Res |= SanitizerKind::Memory;
   Res |= SanitizerKind::Vptr;
   Res |= SanitizerKind::SafeStack;
   if (IsX86_64 || IsMIPS64 || IsAArch64)
     Res |= SanitizerKind::DataFlow;
   if (IsX86_64 || IsMIPS64 || IsAArch64 || IsX86 || IsArmArch || IsPowerPC64)
     Res |= SanitizerKind::Leak;
   if (IsX86_64 || IsMIPS64 || IsAArch64 || IsPowerPC64)
     Res |= SanitizerKind::Thread;
-  if (IsX86_64 || IsMIPS64 || IsPowerPC64 || IsAArch64)
-    Res |= SanitizerKind::Memory;
   if (IsX86_64 || IsMIPS64)
     Res |= SanitizerKind::Efficiency;
   if (IsX86 || IsX86_64)
     Res |= SanitizerKind::Function;
   if (IsX86_64 || IsMIPS64 || IsAArch64 || IsX86 || IsMIPS || IsArmArch)
     Res |= SanitizerKind::Scudo;
   if (IsX86_64 || IsAArch64)
     Res |= SanitizerKind::HWAddress;