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

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-arm64-windows-msvc` running on `linaro-armv8-windows-msvc-04` while building `clang,llvm` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/161/builds/1124

Here is the relevant piece of the build log for the reference:
```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'Clang :: PCH/unsafe-buffer-usage-pragma-pch-cross-files-2.cpp' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
rm -rf C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\PCH\Output\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp.tmp
# executed command: rm -rf 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\PCH\Output\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp.tmp'
# RUN: at line 2
mkdir -p C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\PCH\Output\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp.tmp
# executed command: mkdir -p 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\PCH\Output\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp.tmp'
# RUN: at line 3
split-file C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\clang\test\PCH\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\PCH\Output\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp.tmp
# executed command: split-file 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\clang\test\PCH\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp' 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\clang\test\PCH\Output\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp.tmp'
# .---command stderr------------
# | split-file: error: C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\clang\test\PCH\unsafe-buffer-usage-pragma-pch-cross-files-2.cpp: permission denied
# `-----------------------------
# error: command failed with exit status: 1

--

********************


```

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