Write the make_global_settings to the error message.

I'm trying to land some GN changes and get this error on various platforms with various configurations. Having the actual values that GYP and GN end up with for the make_global_settings will make troubleshooting much faster.

R=maruel@chromium.org

Review URL: https://codereview.chromium.org/104923014

git-svn-id: http://gyp.googlecode.com/svn/trunk@1827 78cadc50-ecff-11dd-a971-7dbc132099af