RFR: 8363910: Avoid tuning for Power10 CPUs on Linux ppc64le when gcc < 10 is used

[Matthias Baesken]

Older gcc version (8, 9) do not support the -mtune=power10 flag. We should set this only when recent gcc versions are used.

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Commit messages:
 - JDK-8363910

Changes: https://git.openjdk.org/jdk/pull/26442/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26442&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8363910
  Stats: 9 lines in 1 file changed: 7 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/26442.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26442/head:pull/26442

PR: https://git.openjdk.org/jdk/pull/26442