I read that as well and Andrew explained that although he wants to do that, it won't happen immediately. There are large projects that rely on this feature and he asked for their input on this topic.
Another thing is that proposed change is to remove clang from the zig distribution. It would still be possible to depend on a zig package that provides an interface to seamlessly compile with system clang.
Note that there would still be an LLVM backend for outputting .bc files (#13265), but the Zig compiler would lack the capability to compile .bc files into object files. LLVM or Clang would need to be installed and invoked separately for that use case.
You'd just need LLVM separately but Zig would still be able to make files that LLVM can handle.
“Clang and GCC cannot do this” this is such a dishonest claim. A certain clang distribution he tried “couldn’t do it”, but that does not mean that clang in general can’t cross-compile. In fact, the reason zig can is LLVM itself. You can build a custom distribution with all your favorite targets from clang (just like you can build a whole compiler for a new language).
The magical thing here are C header files. While it is certainly possible to crosscompile using traditional tooling, what zig does here is an all-in-one package that lets you cross-compile not only to a different architecture, but a different libc or operating system. Most impressive is it's support for selecting target glibc version.
Actually there was some effort (I think currently on halt) to make those headers usable outside of zig. So yeah, it's not a thing that is (or rather must be) zig specific, but right now zig is the only language that does that AFAIK
Like I said - you can build a distribution of LLVM with your favorite targets, including sysroots and have it cross compile with ease (or you can download toolchains that others built). What zig does is not special and it is highly misleading (and needlessly contrarian) to claim that clang/LLVM is not capable of doing the same when the very thing enabling zig to do this is LLVM.