Fix char_traits functions for GCC compatibility.

GCC 4.9 fails to inline these functions at -O1 because they are used
indirectly. Declare them as inline instead of always_inline. Discussion
in GCC bugreport: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63220
[IndVarSimplify] Partially revert r217953 to see if this fixes the bots.

Specifically, disable widening of unsigned compare instructions.