GCC front-ends

There is and there never was anything significantly wrong with GCC. If all these projects [1] managed to work with GCC, it means to me that there is nothing significantly wrong with. The only reason for Apple’s switch to LLVM then (I am not going into battle on merits between LLVM and GCC *now*, that’s a different story) was Steve Job being a control freak, who cannot live without having complete toolset under his control, and perhaps him taking revenge on GCC for forcing him to give up on the Objective-C front end [2].

[1] https://en.wikipedia.org/wiki/GNU_Compiler_Collection#Sup...
[2] https://github.com/JoshCheek/clisp/blob/master/doc/Why-CL... and https://www.gnu.org/philosophy/pragmatic.html