handy.h: #define one macro in terms of another

These two macros are equivalent as folding and lowercasing are the same
for this input domain.  Better to say so rather than to replicate the
definitions.

handy.h

@@ -2015,7 +2015,7 @@ END_EXTERN_C
 
 #  define toLOWER_LC(c)	(isascii(c) ? tolower(c) : (c))
 #  define toUPPER_LC(c)	(isascii(c) ? toupper(c) : (c))
-#  define toFOLD_LC(c)	(isascii(c) ? tolower(c) : (c))
+#  define toFOLD_LC(c)          toLOWER_LC(c)
 
 #endif