Revert r304285, r304297.

r304285 - [sanitizer] Avoid possible deadlock in child process after fork
r304297 - [sanitizer] Trying to fix MAC buildbots after r304285

These changes create deadlock when Tcl calls pthread_create from a
pthread_atfork child handler. More info in the original review at
https://reviews.llvm.org/D33325

llvm-svn: 304735