RFR: 8303604: Passing by-value structs whose size is not power of 2 doesn't work on all platforms (mainline) [v2]

[Jorn Vernee]

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> Port of: https://github.com/openjdk/panama-foreign/pull/806 which fixes an issue with passing structs whose size is not a power of two on SysV and AArch64 platforms.

Jorn Vernee has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains four commits:

 - Merge branch 'master' into OOB
 - 8303017: Passing by-value structs whose size is not power of 2 doesn't work on all platforms
   
   Reviewed-by: mcimadamore
 - remove byteWidthOfPrimitive for now
 - 8302990: Reduce duplication in test code
   8293827: Padding computed by CallGeneratorHelper can be incorrect
   
   Reviewed-by: mcimadamore

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Changes: https://git.openjdk.org/jdk/pull/12863/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12863&range=01
  Stats: 705 lines in 11 files changed: 652 ins; 2 del; 51 mod
  Patch: https://git.openjdk.org/jdk/pull/12863.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12863/head:pull/12863

PR: https://git.openjdk.org/jdk/pull/12863