[jdk21u-dev] RFR: 8340804: doc/building.md update Xcode instructions to note that full install is required

[George Adams]

Hi all,

This pull request contains a backport of commit [b639661e](https://github.com/openjdk/jdk/commit/b639661e797fb52ce32ce397a153c886fdc40f53) from the [openjdk/jdk](https://git.openjdk.org/jdk) repository.

The commit being backported was authored by George Adams on 24 Sep 2024 and was reviewed by Erik Joelsson and Julian Waters.

Thanks!

Applies cleanly other than the fact that the minimum supported version is Xcode 8 (also some other html wasn't properly converted so my pandoc run tweaked it slightly)

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Commit messages:
 - Backport b639661e797fb52ce32ce397a153c886fdc40f53

Changes: https://git.openjdk.org/jdk21u-dev/pull/1019/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1019&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340804
  Stats: 14 lines in 2 files changed: 2 ins; 4 del; 8 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1019.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1019/head:pull/1019

PR: https://git.openjdk.org/jdk21u-dev/pull/1019