Clang: Silence warnings

With GCC >=4.7 Clang generates a lot of noise with various compiler flags,
and can even break the builds when using Flags like Graphite.  This can be
reproduced by doing the following:

Setting TARGET_EXTRA_CFLAGS with Graphite flags such as these
TARGET_EXTRA_CFLAGS +=  -fgraphite-identity \
                        -floop-block \
                        -floop-strip-mine \
                        -ftree-loop-distribution \
                        -ftree-loop-linear

Causes the following errors to occure and the builds to fail:

clang: error: argument unused during compilation: '-fgraphite-identity'
                                                  '-floop-block'
                                                  '-floop-strip-mine'
                                                  '-ftree-loop-distribution'
                                                  '-ftree-loop-linear'

Silence the errors by passing the -Qunused-arguments for CFLAGS

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
rs: Fix RS_VERSION define

Commit 51dc7a27a8749d4ad43169bf39d4378529e132cd broke the RS_VERSION
define by setting LOCAL_CFLAGS := something after the addition of
LOCAL_CFLAGS += -DRS_VERSION=...

Make sure the := definition occurs before the += amendment.

Change-Id: I320ae9215f3ef2982c707a6ecaf5a14880ffa036
Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>