Porting D to custom OS

[kinke]

On Saturday, 22 February 2020 at 13:20:40 UTC, IGotD- wrote:
> Do we have any guide for OS porting?

I'd suggest to first hack the compiler, so that it doesn't 
predefine the host OS, but a new version for your OS (and check 
whether predefining `version (Posix)` is appropriate or not). 
That way, you'll hit static asserts when compiling 
druntime/Phobos, where OS-specific parts don't handle the new OS 
yet. Once all compile errors are fixed, you can then move on to 
compiling and linking the druntime/Phobos test runners, fixing 
all linker errors along the way, and finally fixing all failing 
unittests, possibly requiring compiler codegen adaptations.