I'd take it as a complement.

Calling something a "disgusting hack," isn't inherently insulting, it is just a description of how well self documenting and obvious its workings are, which in this case is not at all. Whereas calling something a "work of art" particularly from Linus is high praise.

And while there is some subjectivity to if something is a "hack" or not, the original author doesn't even seem to contend that too much. They were more interested in pointing out that this method likely works across compilers (since it relies on less undefined behaviour than it might first appear).

In any case, it is a neat trick, that I wouldn't want to run across in a codebase since I'd have to spend too long figuring it out.