RFR: 8294281: Allow warnings to be disabled on a per-file basis

[Magnus Ihse Bursie]

There have been a long-standing need to be able to disable individual warnings, not only per library, but also per C/C++ file in a library.

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Commit messages:
 - 8294281: Allow warnings to be disabled on a per-file basis

Changes: https://git.openjdk.org/jdk/pull/10408/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10408&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294281
  Stats: 7 lines in 1 file changed: 5 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/10408.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10408/head:pull/10408

PR: https://git.openjdk.org/jdk/pull/10408