[clang] [Win/X86] Make _m_prefetch[w] builtins to avoid winnt.h conflicts (PR #115099)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `cross-project-tests-sie-ubuntu` running on `doug-worker-1a` while building `clang` at step 5 "build-unified-tree".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/181/builds/12972

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

```
Step 5 (build-unified-tree) failure: build (failure)
0.003 [165/5/1] Copying clang's prfchwintrin.h...
0.004 [165/4/2] Copying clang's xmmintrin.h...
0.014 [165/3/3] Building BuiltinsX86.inc...
FAILED: tools/clang/include/clang/Basic/BuiltinsX86.inc /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/tools/clang/include/clang/Basic/BuiltinsX86.inc 
cd /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build && /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/bin/clang-tblgen -gen-clang-builtins -I /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/clang/include/clang/Basic -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/clang/include -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/tools/clang/include -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/build/include -I/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/llvm/include /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/clang/include/clang/Basic/BuiltinsX86.td --write-if-changed -o tools/clang/include/clang/Basic/BuiltinsX86.inc -d tools/clang/include/clang/Basic/BuiltinsX86.inc.d
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu/llvm-project/clang/include/clang/Basic/BuiltinsX86.td:147:7: error: Unexpected header name
  def _m_prefetch : X86LibBuiltin<"void(void *)">;
      ^
0.015 [165/2/4] Building CXX object tools/llvm-config/CMakeFiles/llvm-config.dir/llvm-config.cpp.o
0.016 [165/1/5] Generating VCSRevision.h
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/115099