On ARMv7 platform, q4 is used, but it isn't declared in clobber list.
It results that q4 isn't preserved automatically by compiler. So that the value of q4 is destroyed.

BUG=418
TESTED=libyuvTest.* on ARM32 with Android
R=fbarchard@google.com

Change-Id: Ib9b5eff8231c5057f4d58f1c4029f5452222af55

Review URL: https://webrtc-codereview.appspot.com/47899004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1353 16f28f9a-4ce2-e073-06de-1de4eb20be90