RFR: 8345179: RISC-V: Add gtests for weak cmpxchg

[Robbin Ehn]

On Mon, 2 Dec 2024 11:55:44 GMT, Fei Yang <fyang at openjdk.org> wrote:

> Hi, Seems this only covers `MacroAssembler::weak_cmpxchg_narrow_value`. Are we going to add testing for this one: `MacroAssembler::cmpxchg_weak`?

As the Zacas is the same as normal cmpxchg and the lr/sc just changes the loop to failure it wasn't my focus.

I can add it if you want, to this PR or a later.

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PR Comment: https://git.openjdk.org/jdk/pull/22476#issuecomment-2511485811