GCC enables -Wtype-limits under -Wextra. Warnings under GCC's -Wtype-limits is covered in Clang by -Wtautological-type-limit-compare and -Wtautological-unsigned-zero-compare.
Since -Wtautological-type-limit-compare can fire spuriously when a type's size is platform-dependent (as detailed in D41512), I am adding only -Wtautological-unsigned-zero-compare to -Wextra.
I should point out that GCC does not throw warnings on pointless unsigned expression comparisons inside templates while -Wtautological-unsigned-zero-compare does. I figure this is a limitation in GCC's implementation and don't think this is an issue but please feel free to let me know if I am mistaken.