Offtopic...

    * Do this with "<0" and ">=0" to only test the sign of the result. A
    * good compiler would generate better code (and a really good compiler
    * wouldn't care). Gcc is currently neither.

[1] can Clang fully compile Linux yet? I haven't followed the updates in a while.

Yes it can [1].

https://docs.kernel.org/kbuild/llvm.html