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).


Review URL:

git-svn-id: 78cadc50-ecff-11dd-a971-7dbc132099af
5 files changed