__tsan::ThreadCreate takes incorrect value for detached argument

Summary:
PTHREAD_CREATE_DETACHED has a different value on Mac OS X. Since both
PTHREAD_CREATE_JOINABLE and PTHREAD_CREATE_DETACHED are non-zero,
`__tsan::ThreadCreate` always creates detached threads.

Reviewers: kcc, samsonov, glider

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10606

llvm-svn: 243151