RFR: JDK-8223309: test failing due to self-assign-overloaded

[Johan Vos]

Using MacOS X 10.14.4 and Xcode 10.2.1 I could not build jdk/jdk anymore:
/Users/johan/openjdk/jdk/test/hotspot/gtest/classfile/test_symbolTable.cpp:62:6:
error: explicitly assigning value of variable of type 'TempNewSymbol' to
itself [-Werror,-Wself-assign-overloaded]
  s1 = s1; // self assignment
  ~~ ^ ~~
1 error generated.

I added an entry to the list of disabled warnings, and that fixed the
problem.

Bug: https://bugs.openjdk.java.net/browse/JDK-8223309

Webrev: http://cr.openjdk.java.net/~jvos/8223309/webrev.00/

- Johan