[jdk11u-dev] RFR: 8210988: Improved handling of compiler warnings in the build

[Andrew Lu]

I backport this for parity with 11.0.24-oracle.

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Commit messages:
 - Backport 09a967ab8143c3d4b0824a0027edaf0e634686ec

Changes: https://git.openjdk.org/jdk11u-dev/pull/2606/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2606&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8210988
  Stats: 111 lines in 6 files changed: 72 ins; 14 del; 25 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2606.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2606/head:pull/2606

PR: https://git.openjdk.org/jdk11u-dev/pull/2606