Move RunGN lower so that modifications to os.environ take effect

Without this the os.environ changes for various default values are
not taken into effect by GN.

R=brettw@chromium.org
BUG=323300

Review URL: https://codereview.chromium.org/139143002

git-svn-id: http://src.chromium.org/svn/trunk/src/build@244963 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

gyp_chromium

@@ -303,14 +303,6 @@ if __name__ == '__main__':
     else:
       args.append(os.path.join(script_dir, 'all.gyp'))
 
-  supplemental_includes = GetSupplementalFiles()
-
-  if not RunGN(supplemental_includes):
-    sys.exit(1)
-
-  args.extend(
-      ['-I' + i for i in additional_include_files(supplemental_includes, args)])
-
   # There shouldn't be a circular dependency relationship between .gyp files,
   # but in Chromium's .gyp files, on non-Mac platforms, circular relationships
   # currently exist.  The check for circular dependencies is currently
@@ -377,6 +369,12 @@ if __name__ == '__main__':
   if syntax_check and int(syntax_check):
     args.append('--check')
 
+  supplemental_includes = GetSupplementalFiles()
+  if not RunGN(supplemental_includes):
+    sys.exit(1)
+  args.extend(
+      ['-I' + i for i in additional_include_files(supplemental_includes, args)])
+
   print 'Updating projects from gyp files...'
   sys.stdout.flush()