Why is it not possible to compile gcc with llvm-gcc? The last time I checked llvm-gcc compiles C and C++ with most GNU extensions.
(And llvm-gcc is based on that version, which is 4.2.1 or something, about 5 years old)
This is problematic for the Cocotron project [1], which is an Xcode-compatible cross-compiler environment for creating Windows/Linux ports of Cocoa apps. Currently one has to revert to Xcode 4.0.2 to build Cocotron's cross-compiler, then upgrade back to 4.2... This is not terribly convenient. (I guess the long-term solution is that Cocotron either has to add a dependency on a non-Apple gcc, or needs to switch to clang for its cross-compiler.)