Add the 'run-gyp' wrapper.

This wrapper does three things:
1. configures an environment like the one used by the www/chromium port,
2. runs Gyp and
3. patches the output Ninja files to use SOAAP.
Improve the 'run-gyp' script slightly.

Make the 'run-gyp' script check for $LLVM_BUILD_DIR and $SOAAP_SOURCE_DIR and patch them into the output build.ninja. Now there is absolutely no need for manual hacking of the build.ninja file!
Also ignore the 'out' directory.

Since this directory is no longer kept in revision control, Git can safely ignore it. This speeds up 'git status' quite a lot.