RFR: 8329331: Intrinsify Unsafe::setMemory [v26]

[Scott Gibbons]

> This code makes an intrinsic stub for `Unsafe::setMemory` for x86_64.  See [this PR](https://github.com/openjdk/jdk/pull/16760) for discussion around this change.
> 
> Overall, making this an intrinsic improves overall performance of `Unsafe::setMemory` by up to 4x for all buffer sizes.
> 
> Tested with tier-1 (and full CI).  I've added a table of the before and after numbers for the JMH I ran (`MemorySegmentZeroUnsafe`).
> 
> [setMemoryBM.txt](https://github.com/openjdk/jdk/files/14808974/setMemoryBM.txt)

Scott Gibbons has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 37 commits:

 - Merge branch 'openjdk:master' into setMemory
 - Fix UnsafeCopyMemoryMark scope issue
 - Long to short jmp; other cleanup
 - Review comments
 - Address review comments; update copyright years
 - Add enter() and leave(); remove Windows-specific register stuff
 - Fix memory mark after sync to upstream
 - Merge branch 'openjdk:master' into setMemory
 - Set memory test (#23)
   
   * Even more review comments
   
   * Re-write of atomic copy loops
   
   * Change name of UnsafeCopyMemory{,Mark} to UnsafeMemory{Access,Mark}
   
   * Only add a memory mark for byte unaligned fill
   
   * Remove MUSL_LIBC ifdef
   
   * Remove MUSL_LIBC ifdef
 - Set memory test (#22)
   
   * Even more review comments
   
   * Re-write of atomic copy loops
   
   * Change name of UnsafeCopyMemory{,Mark} to UnsafeMemory{Access,Mark}
   
   * Only add a memory mark for byte unaligned fill
 - ... and 27 more: https://git.openjdk.org/jdk/compare/6d569961...1122b500

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Changes: https://git.openjdk.org/jdk/pull/18555/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18555&range=25
  Stats: 507 lines in 36 files changed: 420 ins; 5 del; 82 mod
  Patch: https://git.openjdk.org/jdk/pull/18555.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18555/head:pull/18555

PR: https://git.openjdk.org/jdk/pull/18555