Makefile.PL supports --libs:

  --libs=<libs>          Use <libs> for running the linker; defaults
                         to the value of "mysql_config --libs" or a gussed
                         value

Instead of patching, use this option, calling manually "mysql_config
--libs" and appending our rpath flags.

Also move `environment` to base part, as it's now same in both
mariadb/mysql versions of the component.