Test handling of empty RULE_INPUT_DIRNAME and fix this on android.

1) Add test coverage for RULE_INPUT_DIRNAME being empty to the
rules-dirname test by adding a new input file in the same directory as
the gyp file.

2) Enable the test on the android backend; to make this easy, drop use
of iostream in the test code since the STL is not in Android's default
include path and just use stdio instead.

3) Fix the android generator to normalise paths correctly so that this
case works.

Unfortunately, MSVC does not handle an empty RULE_INPUT_DIRNAME and there's
no obvious way to fix it, so this will have to remain unsupported there.

BUG=
R=thakis@chromium.org

Review URL: https://codereview.chromium.org/255853002

git-svn-id: http://gyp.googlecode.com/svn/trunk@1907 78cadc50-ecff-11dd-a971-7dbc132099af