RFR: 8340804: doc/building.md update Xcode instructions to note that full install is required [v2]

[George Adams]

On Tue, 24 Sep 2024 12:59:15 GMT, Julian Waters <jwaters at openjdk.org> wrote:

>>> You can make it a link using markdown `[]()` syntax.
>> 
>> yeah I'll do that
>
> I will approve once this is fixed, looks good

updated PTAL

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PR Review Comment: https://git.openjdk.org/jdk/pull/21154#discussion_r1773305793