LLVM is a better codebase than GCC despite all that. There is a real technical reason to not go with GCC as I have elaborated on above, the GCC codebase really does have its warts even if it's remarkably clear considering how old it is in places. Just read the code. It's obvious that LLVM has been structured around being consumed as a library, whereas GCC was famously not designed to do that - e.g. LOTS of preprocessor magic versus templates, it's a bit 1980s even if they have done a superb job cleaning it up.
I am a GCC fanboy too, but just be realistic.
Also GCC really needs a kick up the arse when it comes to onboarding new contributors and CI etc. They don't need to go full webscale but I think there's a real risk that GCC ends up being maintained by an increasingly small group of people who eventually just die/retire-off.
The way GCC is tested is quite dumb too, things are pulled but then weeks later someone finds out it failed on such and such a a target because they happened to run the testsuite. It's not terrible but I can't imagine it encourages new contributors.