[toolchain] disable -Wtautological-compare for clang

[Gerald Pfeifer]

On Tue, 18 Oct 2011, Matthias Andree wrote:
>> any chance we could disable -Wtautological-compare for clang? i don't 
>> think comparing an unsigned int against < 0 is worth a warning. 
>> actually it's always nice to have such a seatbelt, in case somebody 
>> changes the type to int and forgets to introduce such a check.
> If your code must be unclean in such a way that it uses deliberately 
> dead code "just in case someone breaks the semantics", can you not use 
> -Wno-tautological-compare in that situation?

It's not as straightforward, sadly, which is why I mentioned I am
on the fence somehow.

  if (TYPE_MIN <= var && var <= TYPE_MAX)

or

  if (var < TYPE_MIN || var > TYPE_MAX)

are not that uncommon, in well written application, and if TYPE_MIN
then evaluates to 0, we'll get a warning.

> Unless someone goes to paranoia mode and sprays unneeded checks like you
> suggest all over the code like an ugly graffity, all such warnings are
> worth investigating.  In code I've hand my eyes and/or hands on, the
> better part of these warnings were pointing to true bugs.

In my experience some were, while others were of the class above.

Gerald