Punybench build process cleanups

Paul preferred the more common '-include' idiom, so this changes the
build to use that.

Also deleted 'arm.mk', which was a NOP file.

BUG=none
TEST=Inspection, and tested building with a non-existant architecture file.

Change-Id: I647d0dfc7d769d747092143026447ef5c45dd363
Signed-off-by: Taylor Hutt <thutt@chromium.org>
4 files changed