c) sort of exists in the form of https://github.com/libav/c99-to-c89 https://github.com/libav/c99-to-c89, although currently it only supports the subset of c99

c) sort of exists in the form of https://github.com/libav/c99-to-c89 https://github.com/libav/c99-to-c89, although currently it only supports the subset of c99 that FFmpeg uses.