armv7-a-neon.mk - append, don't replace... and do some flag massaging

fixed to reflext:

commit 12e0b497cdfe40fe6d7c3431810a376f4bb23c8a
Author: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>
Date:   Sat Jul 14 14:25:08 2012 +0159

    build: Don't work around cortex-a8 issues when targeting a9 only

    Don't work around cortex-a8 issues when other compiler flags
    show we want to target cortex-a9 only

    Change-Id: If5a077243fc15298fbcbe2ffc857b5e961dd29da
    Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>

Change-Id: Ia80a10820cf6d547edfeb662524a338a24670eb5