Agreed that it is better to preserve the input text. Agreed that a warning is indicated, but as Stefano suggested, I think the warning should only be given if -Wportability is enabled (which it is by default, I gather), not unconditionally. From our manual:
`portability' Portability issues (e.g., use of `make' features that are known to be not portable). which, so far as I can see, is what is being dealt with here. --thanks, karl.