There is a commonly used library that interposes the write call, and is
interposed itself. When running with `TSAN_OPTIONS=verbosity=(1|2)`,
this leads to a thread locking itself, resulting in the program hanging.
This patch adds a new flag `lock_during_write` to TSan (on Apple
platforms only) that, when set, allows interceptors to be bypassed
during calls to write. The flag can be inherited by children, or not,
depending on the value.
rdar://157565672
9abd6f22d4