- Alpine Linux
- Arch Linux
- Debian, Ubuntu (on for most arches)
- Fedora does it via spec files globally, not via toolchain
- Gentoo (on for almost every arch by default, obviously in Gentoo you can toggle it easily if you want)
- openSUSE has an interesting gcc-pie package instead which provides a spec file
- Void Linux
- Arch Linux has patched it in (on by default) for Clang for a while
- Gentoo wanted to use it sooner but was waiting for an upstream acceptable patch to avoid rebasing, since 14+ is on by default
- Chimera Linux and any LLVM based musl distros will be using it as it is forced on for musl in LLVM anyway
Most distributions do not use an LLVM-based toolchain by default because this mostly (until very very recently) required using non-glibc. Hence there has been less importance or regard for what LLVM's default was until recently because it was not used as a system compiler.