RFR: 8321542: C2: Missing ChaCha20 stub for x86_32 leads to crashes

[Jamil Nimeh]

This fix corrects an oversight in the ChaCha20 intrinsics delivered by JDK-8247645.  An ifdef guard is now part of the x86 ChaCha20 intrinsics code which disables them by default on 32-bit platforms, as this architecture was not part of the feature delivery.

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Commit messages:
 - Adjust 32-bit warning text
 - C2: Missing ChaCha20 stub for x86_32 leads to crashes

Changes: https://git.openjdk.org/jdk/pull/17072/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17072&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321542
  Stats: 8 lines in 1 file changed: 8 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17072.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17072/head:pull/17072

PR: https://git.openjdk.org/jdk/pull/17072