tsan: unbreak windows build

Currently it fails with:

# Testing race detector.
race_windows_amd64.syso:gotsan.cc:(.text+0x4d89): undefined reference to `__imp_SymGetModuleBase64'
race_windows_amd64.syso:gotsan.cc:(.text+0x4d90): undefined reference to `__imp_SymFunctionTableAccess64'
race_windows_amd64.syso:gotsan.cc:(.text+0x4dd8): undefined reference to `__imp_StackWalk64'
x86_64-w64-mingw32/bin/ld.exe: race_windows_amd64.syso
: bad reloc address 0x10 in section `.data'
collect2.exe: error: ld returned 1 exit status

llvm-svn: 216875