Clang: Silence warnings (1/2)

Clang generates a lot of noise with various compiler flags,
and can even break the builds.

Causes the following warning with some flags:

"clang: error: argument unused during compilation"

Silence the warnings by passing the -Qunused-arguments for LOCAL_CFLAGS

* Patch Set 1:  Initial import of this change:
  http://review.android.git.linaro.org/#change,3379

* Patch set 2:  Make a configurable BoardConfig option
                To enable add TARGET_ARM_OPTIMIZATIONS := true to
                your BoardConfig.mk of your ARM device

Singed-off-by: Paul Beeler <sparksco@gmail.com>