While using mutrace, the phtread-rwlock based isc_rwlock implementation
would be all tracked in the rwlock.c unit losing all useful information
as all rwlocks would be traced in a single place. Rewrite the
pthread_rwlock based implementation to be header-only macros, so we can
use mutrace to properly track the rwlock contention without heavily
patching mutrace to understand the libisc synchronization primitives.
0492bbf590