RFR: 8304434: [AIX] Update minimum xlclang version

[Tyler Steele]

Minor changes to the build system to recognize and warn that an incompatible toolchain is detected.

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Commit messages:
 - Set xlc toolchain minimum version

Changes: https://git.openjdk.org/jdk/pull/13086/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13086&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304434
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13086.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13086/head:pull/13086

PR: https://git.openjdk.org/jdk/pull/13086