Indeed, 4.2.1 was the last GPLv2 version. OpenBSD still uses it (w/ patches) for a few platforms, for example.

/bsd.own.mk:GCC4_ARCH=alpha hppa m88k sh sparc64

The rest have already been migrated to LLVM/Clang 22 by default (except sparc64 below, that's experimental).

./bsd.own.mk:CLANG_ARCH=aarch64 amd64 arm i386 mips64 powerpc powerpc64 riscv64 sparc64