Adding ccache-like output caching to dmd

[Per Nordlöw]

On Tuesday, 29 December 2020 at 19:26:20 UTC, Per Nordlöw wrote:
> If we, in dmd, during the initial (uncached) build log all the 
> imported files including string imports and output them to a 
> cache description together with their individual content hashes 
> and pessimistically rebuild every time anything changes I don't 
> see how this can be an issue. Can you elaborate on which case 
> I've missed?

Thanks, John Colvin for your thorough answer.
Both I and others will greatly benefit from me making my language 
as formal as yours. ;)