Makefiles should work for arbitrary SDKs and architectures on Apple ports

Makefiles should work for arbitrary SDKs and architectures on Apple ports
https://bugs.webkit.org/show_bug.cgi?id=107863

Patch by David Farler <dfarler@apple.com> on 2013-02-07
Reviewed by Mark Rowe.

.:

* Makefile:
Allow SDKROOT, ARCHS outside of $(ARGS).
Setting ARCHS => ONLY_ACTIVE_ARCH=NO.
* Makefile.shared: options to webkitdirs based on SDKROOT
* Source/Makefile: don't build WebKit2 for iOS

Tools:

* DumpRenderTree/Makefile: SDKROOT=iphone* => -target All-iOS
* Makefile: Only build some projects for iOS

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142207 268f45cc-cd09-0410-ab3c-d52691b4dbfc