Have a step that takes the SHA256 or similar of $CC, make that a dependency. You’d need slightly more advanced make features if you want to make it “pretty” (and not just, say, touch a file through some shell code comparison), but this is a slightly more advanced request.

Or potentially just specify the path to $CC itself as dependency? Presumably, if the C compiler changes, the timestamp of its executable does too. (Bad if it goes backwards, though.)