[PING^4] [PATCH] [AArch64, NEON] Improve vmulX intrinsics

[Jiangjiji]

Hi, 
  This is a ping for: https://gcc.gnu.org/ml/gcc-patches/2015-03/msg00772.html
  Regtested with aarch64-linux-gnu on QEMU.
  This patch has no regressions for aarch64_be-linux-gnu big-endian target too. 
  OK for the trunk? 

Thanks.
Jiang jiji