tkchia [0] has been working on getting gcc to emit 16-bit clean code (no 32-bit code prefixes) along with ancillary tooling like binutils, a couple different libc's, and some of the things you'd expect from a 16-bit x86 C compiler like far pointers and DOS-specific libc functions [0]. The use case is to build the FreeDOS Kernel and ELKS 16-bit Linux Kernel from a 32-bit or 64-bit Linux system.

[0] https://github.com/tkchia/gcc-ia16

[1] https://github.com/tkchia/build-ia16/releases