[Issue 12758] allow file names with hyphens

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=12758

--- Comment #4 from bearophile_hugs at eml.cc ---
(In reply to Tom Browder from comment #3)

> I know it may be easier to rename the file
> but I still think the capability should be there.

I think the little convenience of not renaming those files could be less
important than allowing D file names that can't be module names.

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