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

[via Digitalmars-d-bugs]

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

--- Comment #19 from Steven Schveighoffer <schveiguy at yahoo.com> ---
(In reply to Steven Schveighoffer from comment #17)
> -c builds .o

Of course, this is wrong :) -c suppresses link.

--