[clang] [AST][RISCV] Preserve RISC-V intrinsic pragma in AST (PR #171981)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-aarch64-darwin` running on `doug-worker-4` while building `clang` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/32917

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: PCH/riscv-rvv-vectors.c' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
rm -rf /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp
# executed command: rm -rf /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp
# note: command had no output on stdout or stderr
# RUN: at line 2
split-file /Users/buildbot/buildbot-root/llvm-project/clang/test/PCH/riscv-rvv-vectors.c /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp
# executed command: split-file /Users/buildbot/buildbot-root/llvm-project/clang/test/PCH/riscv-rvv-vectors.c /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp
# note: command had no output on stdout or stderr
# RUN: at line 6
/Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/clang -cc1 -internal-isystem /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/lib/clang/22/include -nostdsysteminc -triple riscv64-linux-gnu -target-feature +v -emit-pch -o /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp/test_pch.pch /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp/test_pch.h
# executed command: /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/bin/clang -cc1 -internal-isystem /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/lib/clang/22/include -nostdsysteminc -triple riscv64-linux-gnu -target-feature +v -emit-pch -o /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp/test_pch.pch /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp/test_pch.h
# .---command stderr------------
# | /Volumes/RAMDisk/buildbot-root/aarch64-darwin/build/tools/clang/test/PCH/Output/riscv-rvv-vectors.c.tmp/test_pch.h:2:10: fatal error: 'riscv_vector.h' file not found
# |     2 | #include <riscv_vector.h>
# |       |          ^~~~~~~~~~~~~~~~
# | 1 error generated.
# `-----------------------------
# error: command failed with exit status: 1

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/171981