title: armv8 inline asm compile fail on xcode 6.2
body: <p>I'm trying to compile a inline asm (in *.h) using Xcode6.2 with target to iPad air2(aarch64)</p>
  
  <pre><code>    int16x8_t tmp16x8_4,tmp16x8_5,tmp16x8_6;
      __asm__("cmgt %v0.8h, %v1.8h, %v2.8h"::"w"(tmp16x8_4), "w"(tmp16x8_5), "w"(tmp16x8_6))
  </code></pre>
  
  <p>but compile failure "invalid operand in inline asm:'cmgt ${0:v}.8h,${1:v}.8h,${2:v}.8h'", I try to add \() while still fail.</p>
  
  <pre><code>    __asm__("cmgt %v0\().8h, %v1\().8h, %v2\().8h"::"w"(tmp16x8_4), "w"(tmp16x8_5), "w"(tmp16x8_6))
  </code></pre>
  
  <p>Any suggestion? Thanks!</p>