[llvm] [RISCV][MC] MC layer support for the experimental zalasr extension (PR #69685)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw requested changes to this pull request.

Please add some regression tests:
+ clang/test/Preprocessor/riscv-target-features.c
+ llvm/test/CodeGen/RISCV/attributes.ll
+ llvm/test/MC/RISCV/attribute-arch.s
+ llvm/test/MC/RISCV/zalasr-valid.s
+ llvm/test/MC/RISCV/zalasr-invalid.s

See also https://reviews.llvm.org/D149248.

https://github.com/llvm/llvm-project/pull/69685