Build WebKit2 before building WebKit

Build WebKit2 before building WebKit
https://bugs.webkit.org/show_bug.cgi?id=129831
<rdar://problem/15920020>

Reviewed by Dan Bernstein.

.:

* Source/Makefile:
* WebKit.xcworkspace/xcshareddata/xcschemes/All Source (target WebProcess).xcscheme:
* WebKit.xcworkspace/xcshareddata/xcschemes/All Source.xcscheme:

Tools:

* Scripts/build-webkit:
Always build WebKit2 and make sure to build it before WebKit when building on Mac.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@165220 268f45cc-cd09-0410-ab3c-d52691b4dbfc