RFR: 8252584: HotSpot Style Guide should permit alignas [v2]

[Julian Waters]

> Add alignas to the permitted features set. Though the corresponding entry mentions this should not be done for classes, there's no actual difference in practice with all our supported compilers, because their nonstandard syntax also has the same limitations and issues with dynamic allocation as the C++ alignas, and including such a restriction of falling back to ATTRIBUTE_ALIGNED in the case of classes in the style guide would ultimately not really serve much of a point

Julian Waters has updated the pull request incrementally with one additional commit since the last revision:

  Rectify issues mentioned in review

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Changes:
  - all: https://git.openjdk.org/jdk/pull/11315/files
  - new: https://git.openjdk.org/jdk/pull/11315/files/791563f1..1813e8c0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11315&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11315&range=00-01

  Stats: 37 lines in 2 files changed: 32 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11315.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11315/head:pull/11315

PR: https://git.openjdk.org/jdk/pull/11315