Fix build on archs where char is unsigned

[frediz]

For that specific source file, just add -fsigned-char for compilation.
This closes #709.

[asmaloney]

Does this change have any consequences for the code in ChamferDistanceTransform.cpp or are you just trying to "get it to compile"?

Adding a specific compile flag for one file is a Bad Idea. If there's a problem with that one file then it should be addressed properly.

[frediz]

It was an implementation of the proposal done here : #709 (comment)
Since the code just expects signed char from what I see, it just tells gcc to use signed chars which corresponds to what the code needs.
A better solution would just be to be more precise and be explicit and use signed char instead of char.
And I actually see that this has been done on master (I was checking the logs provided in the bug)...
but the bug #709 has not been closed then.
So, sorry for the noise, nothing to be done.
Thanks for your time.

[asmaloney]

No problem!

Thanks for taking the time to look into it.