RFR: 8155701: The compiler fails with an AssertionError: typeSig ERROR

[Srikanth Adayapalam]

Make sure javac issues suitable diagnostics for types not found in the class path

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Commit messages:
 - 8155701: The compiler fails with an AssertionError: typeSig ERROR

Changes: https://git.openjdk.java.net/jdk/pull/8414/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8414&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8155701
  Stats: 119 lines in 2 files changed: 116 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8414.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8414/head:pull/8414

PR: https://git.openjdk.java.net/jdk/pull/8414