RFR: 8314488: Compile the JDK as C++17 [v2]

[Julian Waters]

> Implementation of [JEP draft: Compile the JDK as C++17](https://bugs.openjdk.org/browse/JDK-8310260)

Julian Waters 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 five additional commits since the last revision:

 - Merge branch 'openjdk:master' into patch-7
 - Revert vm_version_linux_riscv.cpp
 - vm_version_linux_riscv.cpp
 - allocation.cpp
 - 8310260

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/14988/files
  - new: https://git.openjdk.org/jdk/pull/14988/files/09cecd7e..a1f21bbd

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14988&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14988&range=00-01

  Stats: 1027205 lines in 9267 files changed: 298949 ins; 587677 del; 140579 mod
  Patch: https://git.openjdk.org/jdk/pull/14988.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14988/head:pull/14988

PR: https://git.openjdk.org/jdk/pull/14988