[8u20] Request for Phase 2 approval for JDK-8036007: javac crashes when encountering an unresolvable interface

[Dan Smith]

Bug report: https://bugs.openjdk.java.net/browse/JDK-8036007
8u patch: http://hg.openjdk.java.net/jdk8u/jdk8u-dev/langtools/rev/a138f9c9ba33
jdk9 reviewers: vromero, jlahoda

8u20 already includes a fix for JDK-8034147 (http://hg.openjdk.java.net/jdk8u/jdk8u-dev/langtools/rev/37c7dbe8efee).  However, this fix depends on JDK-8036007.  Without it, the test included with JDK-8034147 fails, and the patch simply replaces one crash with another.

Benefits of backport: eliminates an (uncommon) crash, fixes a failing test
Risks of backport: none -- it's a one-line change that _only_ affects invocations that would otherwise crash with an AssertionError

—Dan