[Sanitizer] First effort to implement atomic_compare_exchange for 1-byte vars on Windows

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@177854 91177308-0d34-0410-b5e6-96231b3b80d8
tsan: add SetEnv() function that can be used in frontends



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@177857 91177308-0d34-0410-b5e6-96231b3b80d8