android: set ASFLAGS as well as CFLAGS.

The Android build system doesn't use CFLAGS for assembly source files,
but gyp expects this. Set LOCAL_ASFLAGS in gyp-generated targets to the
same as LOCAL_CFLAGS.

BUG=
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/163433002

git-svn-id: http://gyp.googlecode.com/svn/trunk@1857 78cadc50-ecff-11dd-a971-7dbc132099af