[msbarnett]

If GCC supported that (and if Xcode supported GCC's support of it), you'd probably tell Xcode to use it the same way you tell Xcode to build with GCC instead of clang: You'd select the option in your project settings.

Nobody's made the claim that Xcode is some kind of magical dynamic IDE that supports arbitrary hypothetical features of arbitrary hypothetical versions of arbitrary compilers that you can mix and match on the fly.

Nevertheless it is the case that Xcode allows you to select between clang and GCC 4.2 backends.

[breser]

GCC support in XCode has been less and less GCC and more and more just the LLVM cleverly disguised as GCC. With XCode5 there is nothing left from the actual GCC project, even gdb has been entirely replaced with lldb. So now if you chose GCC in XCode you're not really using GCC at all.