If you are targeting armv4t/armv5/armv6k+vfp (or armv7 but not optimized for it) for Aarch32, or Armv8.0-A and are fine with newlib, then devkitARM and devkitA64, respectively, get the job done and ship GCC 15.1.

There is also devkitPPC, shipping with the same toolchain (and which additionally has some Obj-C support iirc).

Custom patches to newlib and consorts (https://github.com/devkitPro/buildscripts/) introduce hooks and WEAK functions that allow to implement standard library functions on almost any platform, on a platform library basis or even on a per-program basis (with some restrictions on lock sizes).