[Issue 13517] Only touch .di generated file if changed

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=13517

--- Comment #4 from Ketmar Dark <ketmar at ketmar.no-ip.org> ---
(In reply to Vladimir Panteleev from comment #3)
> That idea only applies if you want to do .di generation as a separate
> compiler invocation from compilation.
and why you wouldn't, having the build tool? speed gain is neglible, and
compiler gains new useless code.

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