there is a undefined symbol for function xmlValidNormalizeString() in valid.c
when build libxml2 lib, don't define MACRO: LIBXML_VALID_ENABLED, then there is a undefined symbol for function xmlValidNormalizeString() in valid.c; because xmlValidNormalizeString()'s implement is under MACRO: LIBXML_VALID_ENABLED, but the place calling xmlValidNormalizeString() don't have MACRO: LIBXML_VALID_ENABLED control.
solution:
move function xmlValidNormalizeString() implement out of MACRO: LIBXML_VALID_ENABLED control.