[toolchain] disable -Wtautological-compare for clang

[Gerald Pfeifer]

On Mon, 17 Oct 2011, Alexander Best 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.

I am on the fence on this one, for when I used the equivalent warning
in GCC this did found a number of real issues that I then addressed for
Wine (as an example).

Gerald