RFR: 8301244: Tidy up compiler specific warnings files [v11]

[Julian Waters]

> Cleans up some code in compilerWarnings_*.hpp files to be slightly neater

Julian Waters has updated the pull request incrementally with one additional commit since the last revision:

  PRAGMA_NONNULL_IGNORED should match other pragma formats

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12255/files
  - new: https://git.openjdk.org/jdk/pull/12255/files/a3185f7c..99f8c3a9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12255&range=10
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12255&range=09-10

  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12255.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12255/head:pull/12255

PR: https://git.openjdk.org/jdk/pull/12255