preproc: return found_path as a constant string
preproc: return found_path as a constant string

Always return found_path as a constant string.  We end up making an
internal copy of it anyway to put in the fullpath hash, so there is no
reason to make a duplicate of it.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

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