RFR: 8291302: ARM32: nmethod entry barriers support [v4]

[Aleksei Voitylov]

> This PR implements nmethod entry barriers for ARM32. It has already been implemented for other ports and is related with JDK-8290025 "Remove the Sweeper".

Aleksei Voitylov has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8291302-3
 - remove membar
 - save float registers
 - 8291302: ARM32: nmethod entry barriers support

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11442/files
  - new: https://git.openjdk.org/jdk/pull/11442/files/02439515..079a1a9b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11442&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11442&range=02-03

  Stats: 81291 lines in 1215 files changed: 38190 ins; 35583 del; 7518 mod
  Patch: https://git.openjdk.org/jdk/pull/11442.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11442/head:pull/11442

PR: https://git.openjdk.org/jdk/pull/11442