An attempt to introduce libmysqlclient.so symbol versioning that is
compatible both with Debian and Fedora all versions: put all symbols into
libmysqlclient_18 version node (as on Debian), but also put aliases of
old symbols into libmysqlclient_16 version node (as on Fedora).

Also use a linker script to create aliases of exported symbols, not
rpm_support.cc source file.