You have a few options in 2017 for making 16-bit DOS games coming from a 32/64-bit GCC background: An old 16-bit compiler like Borland C or Turbo C; OpenWatcom which can compile to a 16-bit output; or probably the best option, a newly-released toolchain based on GCC 6.2 available here: https://blogs.mentor.com/embed... (if the link didn't make it through, google for "Sourcery CodeBench Lite for IA16").
My DOS retrocoding is in a mix of Turbo Pascal and assembler, as the TP IDE allows coding/debugging on the old hardware itself. But I'm old, and quite insane.