<https://webkit.org/b/90090> build-webkit should verify that your tools are up-to...

<https://webkit.org/b/90090> build-webkit should verify that your tools are up-to-date

Tools:

Enforce a minimum OS version of 10.7.5 and Xcode version of 4.6.

Reviewed by David Kilzer.

* Scripts/webkitdirs.pm:
(checkRequiredSystemConfig):

Websites/webkit.org:

Update references on webkit.org to mention Xcode 4.6 as the minimum version.

Reviewed by David Kilzer.

* building/debug-mac-uiprocess.html:
* building/tools.html:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@156208 268f45cc-cd09-0410-ab3c-d52691b4dbfc