tsan: fix windows build

Currently fails as:

gotsan.cc: In function 'void* __sanitizer::__libc_memalign(__sanitizer::uptr, __sanitizer::uptr)':
gotsan.cc:6194:50: error: 'posix_memalign' was not declared in this scope
   uptr error = posix_memalign(&p, alignment, size);

Windows does not provide posix_memalign.

llvm-svn: 276107