Ninja: Use native slashes to pass rsp files
In cmNinjaNormalTargetGenerator use ConvertToNinjaPath for rsp files.
Some tools on Windows (Embarcadero linkers, in this case) can't handle forward slashes in paths to rsp files.
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In cmNinjaNormalTargetGenerator use ConvertToNinjaPath for rsp files.
Some tools on Windows (Embarcadero linkers, in this case) can't handle forward slashes in paths to rsp files.