[CMake][tsan] Compile .S files for tsan as C instead of CXX.
[CMake][tsan] Compile .S files for tsan as C instead of CXX.

Using CXX breaks if you add -stdlib=libc++ to CMAKE_CXX_FLAGS.

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@164422 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt