[Issue 24668] ImportC: C files have no way to set module name

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24668

--- Comment #1 from dave287091 at gmail.com ---
I think the fix is to just set the module name to the import path. In other
words `a/foo.c` implies a `module a.foo;` declaration.

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