[jdk23u] RFR: 8340804: doc/building.md update Xcode instructions to note that full install is required

Tue Sep 24 21:41:13 UTC 2024

Since JDK17 there has been a dependency on metal in the macOS builds which is only available as part of the full Xcode IDE (rather than command-line tools). We currently recommend only installing the command-line tools in the building.md doc which is incorrect.

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Commit messages:
 - Backport b639661e797fb52ce32ce397a153c886fdc40f53

Changes: https://git.openjdk.org/jdk23u/pull/121/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk23u&pr=121&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340804
  Stats: 11 lines in 2 files changed: 0 ins; 5 del; 6 mod
  Patch: https://git.openjdk.org/jdk23u/pull/121.diff
  Fetch: git fetch https://git.openjdk.org/jdk23u.git pull/121/head:pull/121

PR: https://git.openjdk.org/jdk23u/pull/121