WL#2394: Code optimization when no UCS2

When no UCS2 is incompiled into the server, it is possible
to optimize the code to make it a bit faster.
Particulary, these comparisions should be be removed:

  if (cs->mbminlen > 1) { ... }


Serg suggested a nice idea how to do it:

Not to add lots of ifdefs around these comparisons,
we can create this macros:

#ifdef HAVE_UCS2
#define have_ucs(X)  (X)
#else
#define have_ucs(X)  (0)
#endif

Then we can use this instead of the above comparisons:

  if (have_ucs(cs->mbminlen > 1)) { ... }

Smart compilers like gcc can optimize this structure by
removing dead code.