[jdk19u] RFR: 8296904: Improve handling of macos xcode toolchain

[Christoph Langer]

The diff to the make file and building.md applied cleanly.
I had to regenerate building.html due to the different version of pandoc used.

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Commit messages:
 - Backport 470f3424fcce0e41b75cccdd5e3a56771cd07ff5

Changes: https://git.openjdk.org/jdk19u/pull/92/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk19u&pr=92&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296904
  Stats: 73 lines in 3 files changed: 29 ins; 4 del; 40 mod
  Patch: https://git.openjdk.org/jdk19u/pull/92.diff
  Fetch: git fetch https://git.openjdk.org/jdk19u pull/92/head:pull/92

PR: https://git.openjdk.org/jdk19u/pull/92