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

[Wang Pengcheng via cfe-commits]

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+# RUN: not llvm-mc -triple riscv32 -mattr=+experimental-zaamo < %s 2>&1 | FileCheck %s
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wangpc-pp wrote:

This can be done in the future, I think.
Current implementation refers to the `Zmmul` (which is a sub-extension of M extension). The case is the same for `Zaamo` and `Zalrsc` I think.

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