Xcode project: adjust settings for debug variants of targets: use default SDK rather than 10.6, native architecture rather than x86_64 + i386, and the default compiler instead of llvm-gcc4.2
This should make the project build out of the box on a wider variety of systems (i.e. without needing the 10.6 sdk)

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1095 af15c1b1-3010-417e-b628-4374ebc0bcbd