Summary:
The Folly `make check` build is broken with Clang on OS X.

This diff fixes the following break in `test/SynchronizedTest.cpp`:

  SynchronizedTest.cpp:150:10: error: thread-local storage is not supported for the current target
    static thread_local int lockCount_;

The problem is clang on OS X doesn't support the `thread_local` extension:

http://stackoverflow.com/a/29929949

so we now use the `FOLLY_TLS` compatibility macro.

When I fixed this, I found the test also failed to compile if `FOLLY_SYNCHRONIZED_HAVE_TIMED_MUTEXES` was `#define`d to `0` (as it is on OS X), so I fixed that.

Reviewed By: mzlee

Differential Revision: D3361215

fbshipit-source-id: e93be6872bcab03090448b9421e502e472f149ff