RFR: 8301244: Replace legacy pragma implementations in HotSpot [v2]

[Julian Waters]

> HotSpot has a few legacy implementations of pragmas in some of its macros, they should be cleaned up and instead use a shared new PRAGMA macro available to all platforms

Julian Waters has updated the pull request incrementally with two additional commits since the last revision:

 - Rename to PRAGMA for gcc
 - Revert macros.hpp

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12255/files
  - new: https://git.openjdk.org/jdk/pull/12255/files/f2734f65..2e5e6a8f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12255&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12255&range=00-01

  Stats: 7 lines in 2 files changed: 3 ins; 4 del; 0 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