RFR [11u] Backport 8223309: test failing due to self-assign-overloaded

[Simon Tooke]

Hello,

This is a request for a review of a backport of  8223309: test failing
due to self-assign-overloaded.
The backport is requested to increase testability using various versions
of the macOS toolchain.
I have modified the patch to work with the build system in jdk11u, and
built and tested it with Xcode 9 and 10.

bug: https://bugs.openjdk.java.net/browse/JDK-8223309
modified patch:
http://cr.openjdk.java.net/~stooke/webrevs/jdk-8223309-jdk11u/00/
original patch: http://hg.openjdk.java.net/jdk/jdk/rev/297ddf282627

Thank you for your time,
-Simon