The LIBSUFFIX directive has a similar function as the {$EXTENSION } and {$LIBPREFIX } compiler directives. directive: it sets the suffix of the library. This is usually used for version numbers: it is simply added to the outputfilename, before the extension.
Example:
will result in a filename libtl-1.2.3.so on linux, or libtl-1.2.3.dll on windows.