Fix MSVC W3 compiler warnings

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@182857 91177308-0d34-0410-b5e6-96231b3b80d8
[asan] Fix r182854: run the unpoison_tls test only on Linux.

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@182858 91177308-0d34-0410-b5e6-96231b3b80d8