RFR: 8302124: HotSpot Style Guide should permit noreturn attribute

[Kim Barrett]

Please review this change to permit the use of noreturn attributes in HotSpot
code.

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2761.pdf
https://en.cppreference.com/w/cpp/language/attributes/noreturn

This will permit such changes as marking failed assertions and the like as
noreturn, permitting the compiler to generate better code in some cases.  This
has benefits even in product builds, since some of the relevant checks occur
in product code (such as `guarantee`, `fatal`, &etc).  It also provides a
solution to the problem described in JDK-8294031, where the potential
continued execution from a failed assertion leads to compiler warnings.

The change is written in such a way that it should be easy to add the
appropriate text for new attributes in the future.  There have been
discussions of adopting C++17, which adds several attributes.

The change to the Style Guide is forward looking, toward a time when more
attributes are available due to the adoption of a newer language standard than
the current C++14.  It is written in such a way that it should be easy to add
the appropriate text for new attributes.

Testing:
I have a prototype of making HotSpot assertions noreturn, which has been run
through mach5 tier1-8 for all Oracle-supported platforms.

This is a modification of the Style Guide, so rough consensus among the
HotSpot Group members is required to make this change. Only Group members
should vote for approval (via the github PR), though reasoned objections or
comments from anyone will be considered. A decision on this proposal will not
be made before Friday 24-Feb-2023 at 12h00 UTC.

Since we're piggybacking on github PRs here, please use the PR review process
to approve (click on Review Changes > Approve), rather than sending a "vote:
yes" email reply that would be normal for a CFV.

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Commit messages:
 - style guide permits noreturn attributes

Changes: https://git.openjdk.org/jdk/pull/12507/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12507&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302124
  Stats: 64 lines in 2 files changed: 52 ins; 12 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12507.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12507/head:pull/12507

PR: https://git.openjdk.org/jdk/pull/12507