This implies both debug and release build by default, unless
one of the --debug or --release config options are passed to
the build-webkit script.

Frameworks can be disabled by passing CONFIG+=webkit_no_framework
to the build-webkit script.

To be able to build both debug and release targets in parallel
we have to use separate output directories for the generated
sources, which is not optimal, but required to avoid race conditions.

An optimization would be to only require this spit-up on Mac.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@43288 268f45cc-cd09-0410-ab3c-d52691b4dbfc