Continue to provide GCC builds with LLVM 19

[ghost]

@brechtsanders You have a recent Clang in your GCC 14.2.0 series. You can always use this Clang to build the latest LLVM.

My goal is to build native GCC.

Along the way - on user request - LLVM was added, but keeping it GCC compatible by using GCC's standard libraries so GCC and LLVM could be mixed within one build environment. But I'm not sure that's such a good idea.

Better would be to have a separate LLVM build environment, with all the native LLVM standard libraries.

But as there already a good LLVM for native Windows available at https://github.com/mstorsjo/llvm-mingw/releases I don't see the point of dedicating my time to that at this point.

Having said that, I have already tried building packages with mstorsjo's LLVM, and it seems some still fail because LLVM doesn't have all the options yet that GCC+binutils have (for example when it comes to Windows resource files).

OK, I have a solution to propose: you can have the latest GCC with LLVM 19 (I don’t think people need the very latest LLVM).