Remember Reflections on Trusting Trust, Ken Thompson’s compiler hack to insert back doors into operating system builds? It dawned on me that Stallman made a critical error in GPL3 - he trusted the compiler.
“The ‘System Libraries’ of an executable work include anything, other than the work as a whole … or a compiler used to produce the work … however, it does not include the work’s System Libraries …” - GPL V3.
As long as you hack the LLVM source code you aren’t afoul with the GPL 3 input.