Re-enable WebRtcIsacfix_AllpassFilter2FixDec16Neon

WebRtcIsacfix_AllpassFilter2FixDec16Neon was disabled due to a Clang
bug. The bug is fixed in current Clang version, re-enable it in this patch.

BUG=4567
R=andrew@webrtc.org, kjellander@webrtc.org
TEST=buildbot build

Change-Id: I71e309cec6caf376181cf9c299c9e8967c9a328e

Review URL: https://codereview.webrtc.org/1194773002 .

Patch from Zhongwei Yao <zhongwei.yao@arm.com>.

Cr-Commit-Position: refs/heads/master@{#9645}
5 files changed