It will be hard to agree with you what "production" even means. I have written and shipped at least one compiler/interpreter (written in plain C). The language

It will be hard to agree with you what "production" even means. I have written and shipped at least one compiler/interpreter (written in plain C). The language wasn't an issue at all. (This compiler doesn't have any meaningful optimizations, but I don't see why that should change the game). GCC and Clang aren't "sold" either, nor is MSVC really. I have never contributed to GCC, but as a fact I have visited plenty of files from its source code, and so far haven't encountered any meaningful use of C++ that couldn't easily be rewritten in plain C. The overwhelming majority of the code would probably compile as C without changes. I'm sure that there are far more meaningful "problems" with the architecture of a compiler written in C that are not the implementation language. For example, GCC is a pain to build (IIRC when I tried many years ago, I gave up).