RFR: 8339156: Use more fine-granular clang unused warnings

[Erik Joelsson]

On Thu, 29 Aug 2024 13:14:35 GMT, Magnus Ihse Bursie <ihse at openjdk.org> wrote:

> Currently, we issue -Wno-unused for all files in clang, which is a rather big sledgehammer to get rid of some warnings that proliferate in a few areas of the build.
> 
> We should instead leave -Wunused turned on (as done by -Wall) and use a much more fine-grained approach to disabling specific warnings in specific files or libraries.
> 
> This is similar to what has been done for gcc in JDK-8339120.

Marked as reviewed by erikj (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/20770#pullrequestreview-2269506759