[llvm] [DAG] Support saturated truncate (PR #99418)

[Craig Topper via llvm-commits]

topperc wrote:

I just submitted #100173 to remove the RISCVISD::VNCLIP* opcodes in favor of the TRUNCATE_VECTOR_VL_*SAT nodes added in this patch. This should allow us to remove the translating from TRUNCATE_VECTOR_VL_*SAT to RISCVISD::VNCLIP*.

https://github.com/llvm/llvm-project/pull/99418