Upstreamings parts of webkit.gyp (step 1)

This is step 1 a multi-step process that is part of the webkit chromium port.

This step includes:
A. Refactoring the wtf, pcre & webcore targets into separate files javascriptcore.gypi and webcore.gyp, which would eventually move upstream.
B. Refactoring the feature_define variables into features.gypi, to allow two sets of feature defines - one for chromium port and one for chromium.
C. Refactoring the config target into config.gyp, since currently both javascriptcore and webcore target depend on it.

Next steps:
2. Eliminate config dependency.
3. Make features.gypi only override built-in variables that live upstream (so we don't have to maintain 2 parallel feature lists).
4. Really move webcore.gyp & javascriptcore.gyp to webkit.org

Review URL: http://codereview.chromium.org/212003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@26584 0039d316-1c4b-4281-b951-d872f2087c98