aarch64: Consolidate NPTL/non versions of clone

At the same time, rely on non-clobbered registers across syscall
so that we eliminate the stack frame that we previously ignored
in the unwind info.
aarch64: Consolidate NPTL/non versions of vfork

At the same time, incorporate the 0 -> 0x80000000 mapping
of the pid expected by raise.c.
S/390: Regenerate ULPs.
aarch64: Remove nptl/vfork.S