[hwasan] Fix HWASAN_WITH_INTERCEPTORS=OFF build on not-android.

Summary:
I'm not aware of any platforms where this will work, but the code should at least compile.
HWASAN_WITH_INTERCEPTORS=OFF means there is magic in libc that would call __hwasan_thread_enter /
__hwasan_thread_exit as appropriate.

Reviewers: pcc, winksaville

Subscribers: srhines, kubamracek, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D61337

llvm-svn: 359914