Improve 64bit memcpy performance for Haswell CPU with AVX instruction

In this patch we take advantage of HSW memory bandwidth, manage to
reduce miss branch prediction by avoiding using branch instructions and
force destination to be aligned with avx instruction.

The CPU2006 403.gcc benchmark indicates this patch improves performance
from 2% to 10%.
Fix -Wundef warning for HAVE_IFUNC
S/390: Revert the jmp_buf/ucontext_t ABI change.
[PATCH] S390: Fix remaining ONE_DIRECTION warning messages

This patch fixes the remaining ONE_DIRECTION warnings for s390 specific conversions.
It defines ONE_DIRECTION to 0 like the patch from Steve Ellcey:
https://www.sourceware.org/ml/libc-alpha/2014-05/msg00039.html

    Changelog:
    * sysdeps/s390/s390-64/utf16-utf32-z9.c
    (ONE_DIRECTION): Define.
    * sysdeps/s390/s390-64/utf8-utf16-z9.c
    (ONE_DIRECTION): Define.
    * sysdeps/s390/s390-64/utf8-utf32-z9.c
    (ONE_DIRECTION): Define.
Split nptl-signals.h out from pthreadP.h
Use __builtin_trap for ABORT_INSTRUCTION.
Add __safe_fatal and use it in __pthread_unwind forwarder fallback.