I got the following error when trying to build PHP 5.6.14/5.6.15 after upgrading to MySQL 5.7:

configure: error: Cannot find libmysqlclient_r under /usr/local/mysql.
Note that the MySQL client library is not bundled anymore!

I added this to my build script in order to create the missing symbolic links:

cd /usr/local/mysql/lib
for f in libmysqlclient.so*; do ln -s $f $(echo $f | sed s/libmysqlclient/libmysqlclient_r/); done
ln -s libmysqlclient.a libmysqlclient_r.a