tsan: align ThreadState to cache line

There are 2 reasons to do this:
1. We place hot data in the first cache line of ThreadState,
this assumed that it's cache-line-aligned but we never actually
enforced it (or it was lost at some point).
2. The new vector clock uses vector instructions and requires
data alignment. Later the new vector clock will be embedded in
ThreadState, then ensuring vector clock alignment will be
impossible w/o ThreadState alignment.

Depends on D110519.

Reviewed By: melver

Differential Revision: https://reviews.llvm.org/D110520