Revert "Logging: Make sure logging machinery is in a consistent state after forking"

The pthread_atfork trick breaks on android, because
pthread_rwlock_unlock detects that it is not the same thread which
locked the lock. This means that the subsequent lock attempt will still
deadlock (only this time it happens deterministically instead of at
random). Reverting to find a better solution.

This reverts commit r316173.

llvm-svn: 316231