[clang] [llvm] [RISCV] Add sifive-p470 processor (PR #102022)

[Min-Yih Hsu via cfe-commits]

mshockwave wrote:

> > LLVM Buildbot has detected a new failure on builder `flang-x86_64-windows` running on `minipc-ryzen-win` while building `clang,llvm` at step 7 "test-build-unified-tree-check-flang".
> > Full details are available at: https://lab.llvm.org/buildbot/#/builders/166/builds/8
> > Here is the relevant piece of the build log for the reference
> 
> What a long reflex arc!

As the icing on the top, I think that buildbot failure has nothing to do with this patch

https://github.com/llvm/llvm-project/pull/102022