That works for Xcode 4.1, which is now out-of-date. The current releases of Xcode, 4.2.x for 10.7 Lion and optionally for 10.6 Snow Leopard, no longer include gcc-4.2, only llvm-gcc and clang.  I am working on completing an extensive set of regression tests for all of the development branches versus the most important set of Xcode/platform options and should have results here later this week.