Fixed Clang warnings

Fixed Clang warnings

Reverts 0073a9c8941a0e04a10035e7cc00ffddc8c0f083

Turns out the C99 standard guarantees a 2's complement representation
for fixed width integers: section 7.20.1.1, paragraph 1:

> The typedef name intN_t designates a signed integer type with width N,
> no padding bits, and a two's complement representation.

The comment was not needed though (those line are fully portable C99),
so I preserved its removal.