This kind of thing shows why ifdefs are usually the wrong tool for multi-target projects.
There should be a platform adapter API instead that defines a shared header with function names for these actions, multiple platform-specific implementation files, and only one of them gets compiled.
That way you could simply ignore the existence of "filesys_amiga.c", and then maybe delete it 50 years from now.
(I realize it's probably not realistic to do such major internal surgery on Make at this point.)
This was one of the brilliant aspect of Knuth's web system: You could have change files that would be applied to the immutable source to manage ports to individual platforms.¹ I really wish that this sort of patching had spread to other programming paradigms.
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1. It works even on somewhat actively developed code since the likely to require porting parts of the program could be clumped together in a web source file and, once isolated, generally saw few if any changes. I remember maintaining the public domain vms change files for the TeX 2–3/MF 1–2 upgrades and as I recall, even with these significant changes to the programs, no updates for the change files were necessary.²
2. Most of the work that I did back then in maintenance was centered around enhancements to the VMS-specific features. For example, rather than having iniTeX be a special executable, instead, iniTeX features could be enabled/disabled at runtime from a single executable.³ Similarly with debug code.
3. This feature appeared soon after in the web2c port of TeX and friends, but I think that Tom Rokicki might have got the idea from me (or else it was a case of great minds thinking alike in the late 80s).
I respectfully disagree to this very common argument against ifdefs, and will also point out that developers who hold this anti-ifdef belief hold it quite strongly! I generally prefer the ifdef-style.
There should be a platform adapter API instead that defines a shared header with function names for these actions, multiple platform-specific implementation files, and only one of them gets compiled.
That way you could simply ignore the existence of "filesys_amiga.c", and then maybe delete it 50 years from now.
(I realize it's probably not realistic to do such major internal surgery on Make at this point.)