RFR: 8307168: Inconsistent validation and handling of --system flag arguments [v4]

[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:

  Update OptionSmokeTest.java

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Changes:
  - all: https://git.openjdk.org/jdk/pull/16264/files
  - new: https://git.openjdk.org/jdk/pull/16264/files/b155a4e4..73e7f0e8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16264&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16264&range=02-03

  Stats: 18 lines in 1 file changed: 0 ins; 17 del; 1 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