[jdk21u] RFR: 8314262: GHA: Cut down cross-compilation sysroots deeper

[Aleksey Shipilev]

Clean backport to improve GHA overheads.

Additional testing:
 - [ ] GHA

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Commit messages:
 - Backport 38687f1a3eb7d1c2e8aa43b85509ab7999fe0e40

Changes: https://git.openjdk.org/jdk21u/pull/61/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=61&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314262
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u/pull/61.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/61/head:pull/61

PR: https://git.openjdk.org/jdk21u/pull/61