Neat, but I wonder what the motivation for this is. I assumed that for the majority of projects ninja itself adds little overhead to the total build time.
I suspect it's more that they don't like C++ and want to use C for everything. Whether that actually translates into a higher quality tool or a more performant tool, we can only imagine.
Though Ninja is implemented in a very moderate C++ style; I'm able to compile it even with GCC <= 4.8; it even seems to compile on pre-C++11 compilers.
There is also Muon [1] for Meson (Python).
There are minimal C compilers written in C around, though, admittedly, not as relevant as GCC/clang/MSVC
As much as I believe this to be true in politics, I think it's really really wrong, if not actively harmful, in tech