Clang is still relevant because LLVM is great, but as a compiler it's mired in a great deal of political hangups and general pickiness. I don't write C++ for a living, but my experience using the GNU C tooling has been much smoother than Clang and Cmake.
I'll admit that both of those projects aren't exactly dead, but it would be a shame if Microsoft/Google/Apple bought Mold and malformed it to their desires.
The CUPS lead author left Apple a couple of years ago, and CUPS development is now mostly focused on Linux under the auspices of the Openprinting organization. (I understand the CUPS lead author still has some side consulting gig in providing bug fixes to Apples version of CUPS.)