Changes the ninja generator to output phony targets for uninteresting targets

This way you can pass these targets to the build system and not get
errors.

BUG=410410
TEST=covered by test now
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/543743003

git-svn-id: http://gyp.googlecode.com/svn/trunk@1973 78cadc50-ecff-11dd-a971-7dbc132099af