RFR: 8286057: Make javac error on a generic enum friendlier [v2]

[Aggelos Biboudis]

> Improves the error message for generic enumerations.

Aggelos Biboudis has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  8286057: Make javac error on a generic enum friendlier

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8677/files
  - new: https://git.openjdk.java.net/jdk/pull/8677/files/7b920a50..0d7db485

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8677&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8677&range=00-01

  Stats: 37 lines in 3 files changed: 0 ins; 36 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8677.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8677/head:pull/8677

PR: https://git.openjdk.java.net/jdk/pull/8677