[11u] RFR : 8266818: Enable AIX build platform to make external debug symbols

[Andrew Leonard]

Please can I get a review and sponsor for this straight backport (bar build
system variable changes) of the jdk-17 patch
http://cr.openjdk.java.net/~aleonard/8266818/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8266818

Tested downstream at Adoptium CI using Xlc v13.1:
https://ci.adoptopenjdk.net/job/build-scripts/job/jobs/job/jdk11u/job/jdk11u-aix-ppc64-hotspot/929/

Many thanks
Andrew