Allow 'script' component to enter a 'built' state

After this pull request merged:

https://github.com/servo/servo/pull/7209

the 'script' component would never enter a 'built' state. In other
words, if one calls `mach build`, lets it complete, then calls `mach
build` again, the 'script' component would rebuild even though we
supposedly just built it. This was due to the `ParserResults.pkl`
getting placed in the `components/script` directory instead of the
output directory, causing cargo to think that there were unbuilt files.

components/script/dom/bindings/codegen/GlobalGen.py

@@ -54,7 +54,8 @@ def main():
     parserResults = parser.finish()
 
     # Write the parser results out to a pickle.
-    with open('ParserResults.pkl', 'wb') as resultsFile:
+    resultsPath = os.path.join(outputdir, 'ParserResults.pkl')
+    with open(resultsPath, 'wb') as resultsFile:
         cPickle.dump(parserResults, resultsFile, -1)
 
     # Load the configuration.