[clang] [llvm] [RISCV] Add Spacemit X100 processor definition (PR #173988)

[Olaf Bernstein via cfe-commits]

camel-cdr wrote:

Reading https://www.spacemit.com/en/news/spacemit-makes-important-breakthroughs-in-risc-v-high-performance-cores/, it sounds like the X100 should enable some of the fusion tuning flags.

I'm not sure how `TuneDLenFactor2` is used by llvm, but it sounds like X100 is VLEN=256 and four issue DLEN=128. While the SiFive cores that currently define `TuneDLenFactor2` are single issue DLEN=VLEN/2.

https://github.com/llvm/llvm-project/pull/173988