[build] Make sure ZLIB paths are appended
[build] Make sure ZLIB paths are appended

Overriding AX_CHECK_ZLIB default if-found-action causes ZLIB include dir
and cflags to not be appended as desired, so building with --with-zlib
was broken.

anthrotype/ots,davelab6/ots,khaledhosny/ots,irori/ots,anthrotype/ots,davelab6/ots,irori/ots