Added signed char spec for numeric_limits; gcc has 3 char types.
Added signed char spec for numeric_limits; gcc has 3 char types.

Gerii/ustl,PetteriAimonen/ustl,Gerii/ustl,msharov/ustl,szastupov/ustl,msharov/ustl,uusirant/ustl-cmake,PetteriAimonen/ustl,NoSuchProcess/ustl,dgruss/ustl,PetteriAimonen/ustl,szastupov/ustl,dgruss/ustl,uusirant/ustl-cmake,NoSuchProcess/ustl