Make gcd_traits<signed char>::make_odd return unsigned int, similar to all other gcd_traits specializations. Also, correct the local variable types that receive the result of make_odd to avoid warnings about unintended conversion.
Please refer to the Boost.Math revision log for details of changes, but in summary:
* New version of gcd/lcm internals by Jeremy Murphy include mixed-binary algorithm and better selection logic.
* Support is now included for gcd's of polynomials.
* Full C++14 constexpr support.
