> The toolchain can be used on either a GNU/Linux® or Microsoft® Windows® host.
Bingo. I love programming for early DOS systems (86, 286, 386) but it's difficult to find a tool-chain that runs on Linux and is able to produce DOS compatible binaries. I think OpenWatcom might but I could not get it to work correctly.
https://www.digitalmars.com/download/freecompiler.html
Source code to the compiler/libraries is also free:
https://github.com/DigitalMars/dmc
https://github.com/DigitalMars/Compiler