Determine how to support 'LEGACY' MSDOS compiler going forward

[LADSoft]

in #297, we are rewriting the compiler into three parts and using shared memory (via CreateFileMapping and friends) to handle communications between the parts.

However, the MSDOS runtime isn't likely to have CreateFileMapping and friends. Assuming it doesn't there are three paths going forward:

1. implement CreateFileMapping and friends in the MSDOS runtime
2. deviate from the current plan for the MSDOS compiler and use conditional compiles to change the behavior for this version of the compiler
3. Auto detect the presence of CreateFileMapping and friends and do a fallback to write to a file in the OS if they aren't there.

These are all beyond the scope of #297 so I'm opening this new issue.

[GitMensch]

I'd suggest to not implement CreateFileMapping in the MSDOS runtime but support for mmap() in the runtime in general - this is very likely also needed for any other non-windows environment later so most of the time put in this shouldn't "feel kind of wasted" for the legacy system dos.

[LADSoft]

so as per #828 my current plan is to retire MSDOS support entirely within a few months

[ghost]

Please correct me if I'm wrong. The current problem seems to be with running the compiler itself on DOS. If this is really the case, then I don't think you need to remove support for DOS. You can always have the compiler running on Windows but cross-compile to DOS.

[LADSoft]

this is on hold for now... if anyone wants it let me know