Revert "Add pthread_self function prototype and make it speculatable."

This reverts commit 143d7445b5dfa2f6d6c45bdbe0433d9fc531be21.

Build breaking

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@303496 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed