Don't try to compile ARM assembly when we're not compiling for ARM.

Change-Id: Ie32df975278f3e35eeacd02a43f16622c026a897
(cherry picked from commit 6c75dbce02862fb173ebe78d6c65b9d195ecdd32)
skia: Rename perf flag

Change-Id: If9f0976d9ba2ec22c4d9f70f203e033662ed0580
(cherry picked from commit 35ab79f2120eb956cc0a4bfde11580546b2b5127)