aclocal and autoconf calls are necessary to build the xhprof php extension

`aclocal` and `autoconf` calls are necessary to build the xhprof php extension in Gentoo.
This is the same situation as with other extensions like `mongo`.
See: http://php.net/manual/en/mongo.installation.php#mongo.installation.gentoo

Not sure, if it affects the build process in other distros.