Fix rwlock error messages to specify the correct function names.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
Workaround pthreads-win32 pthread_rwlock_init limitation.

On Windows, pthreads-win32 returns EINVAL if you specify an attribute when
calling pthread_rwlock_init. Work around this by only specifying the attribute
when FIO_HAVE_PSHARED_MUTEX is defined.

Signed-off-by: Jens Axboe <axboe@kernel.dk>