add test for tautological-compare error

[PeterHajdu]

I'm not sure if you would like to add a test for it, but I've managed to reproduce the previous issue. Also I don't know your test suit / case naming conventions, so don't hesitate to throw this one out if you think.

[Rapptz]

I don't think a test case for this is needed since it's a compiler dependent error due to -Werror rather than a hard compilation error. I appreciate the patch though :)

[PeterHajdu]

ok, you're welcome.