This adds a workaround that zeroes out semaphores before they are
initialized. Some versions of sem_init (e.g. GLIBC_2.0) fail to fully
zero out the semaphore, leading to {errno == ENOSYS} with subsequent
sem_timedwait calls.

R=machenbach@chromium.org
BUG=chromium:536813
LOG=n

Review URL: https://codereview.chromium.org/1407463002

Cr-Commit-Position: refs/heads/master@{#31232}