RFR: 8307168: Inconsistent validation and handling of --system flag arguments [v2]

[Christian Stein]

> Please review these changes that fix a bug in `javac`'s validation and handling of `--system` flag arguments.

Christian Stein has updated the pull request incrementally with one additional commit since the last revision:

  Added test cases and "unrolled" boolean expression

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16264/files
  - new: https://git.openjdk.org/jdk/pull/16264/files/190e200b..48d3c04e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16264&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16264&range=00-01

  Stats: 65 lines in 2 files changed: 52 ins; 4 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/16264.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16264/head:pull/16264

PR: https://git.openjdk.org/jdk/pull/16264