[clang] [llvm] [RISCV] Add support for -mtune=andes-45-series (PR #142900)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

> > LLVM Buildbot has detected a new failure on builder `arc-builder` running on `arc-worker` while building `clang,llvm` at step 6 "test-build-unified-tree-check-all".
> > Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/17084
> > Here is the relevant piece of the build log for the reference
> 
> I’m not sure why the test fails to find the string andes-45-series, since it works fine on my local machine.

I also noticed that the this specific buildbot, arc-builder, tends to throw confusing errors like this when we added a new `-mcpu`.

https://github.com/llvm/llvm-project/pull/142900