Outdated Book/php7/build_system/building_php.rst

The Book/php7/build_system/building_php.rst seems outdated. For example, this sentence `If you are building from the git repository, the first thing you’ll have to do is run the ./buildconf script. This script does little more than invoking the build/build.mk makefile, which in turn calls build/build2.mk.`. The file `build/builld.mk` is for php5, but php7 has been removed.