[TSan] #include header instead of forward declaring interceptees
os_unfair_lock_lock was introduced in macOS 10.12. This means that you have to upgrade your builder to use at least SDK 10.12. However, I am not aware of any reason not to use the most recent SDK (10.15) for building. Let me know if you have any issues with this.
The lowest supported version for running is set via the "deployment target". AFAIR, this is set to 10.9 for compiler-rt.