y2038: Convert mtx_timedlock to support 64 bit time

y2038: Convert mtx_timedlock to support 64 bit time

The mtx_timedlock function has been converted to support 64 bit time.
It was also necessary to provide Linux specific copy of it to avoid
problems on i686-gnu (i.e. HURD) port, which is not providing
pthread_mutex_timedlock() supporting 64 bit time.

The mtx_timedlock is a wrapper on POSIX threads to provide C11 standard
threads interface. It directly calls __pthread_mutex_timedlock64().

Build tests:
./src/scripts/build-many-glibcs.py glibcs

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>