RFR: 8265666: Enable AIX build platform to make external debug symbols

[Andrew Leonard]

This change simply enables the specification of configure args to build
external AIX debug symbols:

--with-native-debug-symbols=external/zipped

Now that we build using XLC/xlclang++ v16+ which supports standard external
.debuginfo generation, it is simply a matter of enabling the option for AIX,
and the rules for the debug info files and copy.

This change has also been tested at AdoptOpenJDK build Jenkins.

Thanks

Andrew