RFR: 8264623: Change to Xcode 12.4 for building on Macos at Oracle

Wed Apr 7 22:35:43 UTC 2021

Switch to Xcode 12.4 for building macosx-x64 at Oracle. The new lldb dependency is needed to ensure that we can collect information when testing on older versions of macOS which do not support Xcode 12.4.

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Commit messages:
 - 8264623: Change to Xcode 12.4 for building on Macos at Oracle

Changes: https://git.openjdk.java.net/jdk/pull/3388/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3388&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8264623
  Stats: 15 lines in 1 file changed: 12 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3388.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3388/head:pull/3388

PR: https://git.openjdk.java.net/jdk/pull/3388