Add a relative source path variable to our gyp build process.

generate_projects

@@ -32,6 +32,7 @@ if __name__ == '__main__':
 	gyp_cmd += ' -G msvs_version=' + msvs_version
 	gyp_cmd += ' -D angle_build_tests=' + ('1' if build_tests else '0')
 	gyp_cmd += ' -D angle_build_samples=' + ('1' if build_samples else '0')
+	gyp_cmd += ' -D angle_relative_src_path=..\\..\\src\\'
 	gyp_cmd += ' ' + os.path.join(script_dir, 'all.gyp')
 
 	print 'Generating projects to' + generation_dir + ' from gyp files...'

src/angle.gypi

@@ -7,6 +7,7 @@
     {
         'angle_code': 1,
         'angle_post_build_script%': 0,
+        'angle_relative_src_path%': '',
     },
     'includes':
     [