RFR: 8355446: Change to Xcode 15.4 for building on macOS at Oracle

[Mikael Vidstedt]

Oracle is updating the version of Xcode for building the JDK on macOS to Xcode 15.4.

Testing: tier1-5

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Commit messages:
 - Update doc/building.md to reflect updated macOS/Xcode versions
 - 8355446: Change to Xcode 15.4 for building on macOS at Oracle

Changes: https://git.openjdk.org/jdk/pull/24862/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=24862&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8355446
  Stats: 8 lines in 3 files changed: 0 ins; 0 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/24862.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24862/head:pull/24862

PR: https://git.openjdk.org/jdk/pull/24862