Zig actually bundles LLVM's Clang, which it uses to compile C with the `zig cc` command. But the long term goal seems to not be so tightly coupled to LLVM, so I'm expecting that to move elsewhere. They still do some clever stuff around compiler-rt, allowing it to be better at cross-compilation than raw Clang, but the bulk of it is mostly just Clang.
There is also another C compiler written in Zig, Aro[1], which seems to be much more complete than TFA. Zig started using that as a library for its TranslateC functionality (for translating C headers into Zig, not whole programs) in 0.16.
They're not planning on dropping Clang.