[jdk21u-dev] RFR: 8338286: GHA: Demote x86_32 to hotspot build only

[Aleksey Shipilev]

This should make GHAs cleaner and more efficient for future backports.

Additional testing:
 - [ ] GHA

-------------

Commit messages:
 - Backport da7311bbe37c2b9632b117d52a77c659047820b7

Changes: https://git.openjdk.org/jdk21u-dev/pull/935/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=935&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338286
  Stats: 19 lines in 1 file changed: 1 ins; 11 del; 7 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/935.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/935/head:pull/935

PR: https://git.openjdk.org/jdk21u-dev/pull/935