Adding support for xlC compiler

In aol.properties file, the xlC properties have been added.
In Linker.java, in getVersion() method, the case of xlC was not handled.
Therefore a warning was generated saying "cannot find version number for
linker". This case is added and the warning is no longer generated.
In VisualAgeLinker.java, in the addImpliedArgs() method, the first
argument 'CCTask task' was missing. So this was not overriding the
addImpliedArgs() method of the AbstractLdLinker. This means that the
generated linking command was "xlc -shared" (which did not work for xlC), instead of the correct "xlc
-qmkshrobj" command. Adding the argument fixed this issue.