[RFC] 3.0 drop musl toolchain

[henderkes]

I would like to drop musl toolchain support for 3.0. It's a pain to compile, it's still an old gcc 13 version and it forces us to host our own black box binaries.

Php compiled statically against musl is slow. Users can compile php staticallly linked against musl with zig.

The only benefit the musl toolchain has is compiling on a glibc system without docker and getting slightly better performance than with zig for php <8.5. Even then it's slower than using docker to use alpine. In my eyes, that's just not worth it.