sdiff: fix wcwidth recursion

sdiff: fix wcwidth recursion

Apparently trying to diff non-UTF8 documents caused a stack overflow.
The culprit was correctly identified by Yonetani as the redefinition
of wcwidth in the wcwidth.c file.  Within that function, it calls itself
recursively forever.  I'm not sure how this would work differently
(macro or not) on another system.

My solution was to stop redefining wcwidth and just create a separate
function, one that will call the system wcwidth function as needed.

reported by: Peter Avalos
http://bugs.dragonflybsd.org/issue2134