C99 (with very few stuff from c11 and WITHOUT ONE BAZILLION EXTENSIONS), is, by far the less worse compromise out-there.

gcc and clang are c++ abominations, and some toxic people did manage to make hard dependent linux (and *BSD) on their zillions of extensions (for linux, right under Linus T. noze).

But we have tinycc(~2 times slower machine code than gcc), cproc/qbe (I get ~70% of gcc speed).

Oh, and don't forget, RISC-V assembly, no global intellectual property lock on this ISA, and nice to code in.