nptl: Move rwlock functions with forwarders into libc

The forwarders were only used internally, so new symbol versions
are needed.  All symbols are moved at once because the forwarders
are no-ops if libpthread is not loaded, leading to inconsistencies
in case of a partial migration.

The symbols __pthread_rwlock_rdlock, __pthread_rwlock_unlock,
__pthread_rwlock_wrlock, pthread_rwlock_rdlock,
pthread_rwlock_unlock, pthread_rwlock_wrlock have been moved using
scripts/move-symbol-to-libc.py.

The __ symbol variants are turned into compat symbols, which is why they
do not receive a GLIBC_2.34 version.