Fix gettid() on Windows.

Accidentally had this all hidden by an #ifndef _WIN32 when I wrote it.

Bug: 19517541

(cherry picked from commit b3a36ca5ee79411c18984b85b224d9285b4468af)

Change-Id: Ifbd5d19e506e7313700e2e29a2dae5736e049844
2 files changed