[clang] [llvm] [RISCV] Add experimental support of Zaamo and Zalrsc (PR #77424)

[Sam Elliott via cfe-commits]

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lenary wrote:

Can we not do this, can we please instead make A imply Zaamo and Zalrsc, and just check for the right sub-extension everywhere? It took a long time to unwind this with C/Zca/Zce, and I'm not sure we get much value from this for people not using integrated assemblers. 

https://github.com/llvm/llvm-project/pull/77424