Someone may chime in and say "but LLVM" - but LLVM could not possibly be written without GCC, as it started as a GCC frontend.

LLVM frankly should not have been written - it is the LLVM's developers duty for the sake of humanity to adopt a free copyleft like the GPLv3-or-later or AGPLv3-or-later, or find and delete all copies of it, but they relentlessly shirk their duty.