I'm trying to setup a VM Ubuntu 64-bit to debug and test, but instructions in build-setup @ PHP are poor and  five years old.

./configure is unable to find libxml2, correctly installed in system /usr/lib/x86_64-linux-gnu/

--with-xmldir-dir=/usr/lib/x86_64-linux-gnu

doesn't help.

....

checking libxml2 install dir... /usr/lib/x86_64-linux-gnu
checking for xml2-config path...
checking for pkg-config... /usr/bin/pkg-config
configure: error: libxml2 not found. Please check your libxml2 installation.