There are consumers of rwlocks, inluding our own libc, that depend on

There are consumers of rwlocks, inluding our own libc, that depend on
a PTHREAD_RWLOCK_INITIALIZER to do for rwlocks what
a similarly named symbol does for statically initialized mutexes.
This symbol was dropped in The Open Group Base Specifications Issue 6
and does not exist in IEEE Std 1003.1, 2003, but it should still be
supported for backwards compatibility.

Pointy hat: mtm