for NPTL where the PID is stored at userlevel and needs to be
reset when CLONE_THREAD is not used.
nptl/
* sysdeps/unix/sysv/linux/alpha/clone.S: New file.
* sysdeps/alpha/tcb-offsets.sym (TID_OFFSET): New.
* sysdeps/alpha/tcb-offsets.sym: New file.
* sysdeps/unix/sysv/linux/alpha/sysdep-cancel.h (SINGLE_THREAD_P):
Use MULTIPLE_THREADS_OFFSET to implement !libpthread !libc version.
* sysdeps/unix/sysv/linux/alpha/lowlevellock.h: Rewrite based
on powerpc version.