RFR: 8314488: Compile the JDK as C++17 [v7]

[Julian Waters]

> Compile the JDK as C++17, enabling the use of all C++17 language features

Julian Waters has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 11 commits:

 - Merge branch 'master' into patch-7
 - Require clang 13 in toolchain.m4
 - Remove unnecessary -std=c++17 option in Lib.gmk
 - Merge branch 'openjdk:master' into patch-7
 - Compiler versions in toolchain.m4
 - Merge branch 'openjdk:master' into patch-7
 - Merge branch 'openjdk:master' into patch-7
 - Revert vm_version_linux_riscv.cpp
 - vm_version_linux_riscv.cpp
 - allocation.cpp
 - ... and 1 more: https://git.openjdk.org/jdk/compare/269163d5...9286a964

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Changes: https://git.openjdk.org/jdk/pull/14988/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14988&range=06
  Stats: 4 lines in 2 files changed: 0 ins; 1 del; 3 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