android: Add a way to override build system variables.

Add a key 'aosp_build_settings' which a target can use to set Android
build system variables in the generated makefile, for edge cases not
directly supported by gyp. aosp_build_settings is a dictionary which
maps variable names to values (values may be integers, strings or lists;
all values will be quoted appropriately for make and lists will be
converted to whitespace-separated form).

BUG=
R=primiano@chromium.org, thakis@chromium.org

Review URL: https://codereview.chromium.org/565743004

git-svn-id: http://gyp.googlecode.com/svn/trunk@1977 78cadc50-ecff-11dd-a971-7dbc132099af
5 files changed