[8u60] Backport RFR: 8072588: JVM crashes in JNI if toString is declared as an interface method

[Andreas Eriksson]

Hi,

Please review this backport of 8072588 
<https://bugs.openjdk.java.net/browse/JDK-8072588>.
Webrev: http://cr.openjdk.java.net/~aeriksso/8072588/webrev.jdk8.00/

Since jdk8 doesn't support native testing with jtreg, I excluded the test.
Otherwise the fix is the same as in jdk9.

Thanks,
Andreas