[clang] [llvm] [RISCV] Add SpacemiT A100 processor definition (PR #174052)

[Mark Zhuang via llvm-commits]

zqb-all wrote:

The SpacemiT website does not yet have information on the A100, so I am unable to include a URL in the commit message for now. I will update it once a URL becomes available.

https://github.com/llvm/llvm-project/pull/174052