Doubtful. Both GCC and LLVM are written in C++ so you have to build a C++ compiler irrespective of whether you actually want one!

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.

You can just use a GCC version < 4.8 or something like e.g. TCC if you want to avoid C++.

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.

Compiling gcc <= 4.8 is an exercise in pain because it needs some kernel headers which were removed.

Not a big issue for someone who maintains his own Linux version, https://github.com/oasislinux/oasis.

Ehhh, the creator also works on a minimalist Linux distro (Oasis) and one of their goals is to build with cproc (a C frontend for the QBE backend), all written in ISO C. He uses Samurai in his distro, so it all fits together pretty well