[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 `clang-aarch64-quick` running on `linaro-clang-aarch64-quick` while building `clang` at step 4 "build stage 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/65/builds/11704

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

```
Step 4 (build stage 1) failure: 'ninja' (failure)
[1/174] Copying clang's prfchwintrin.h...
[2/174] Copying clang's xmmintrin.h...
[3/174] Building BuiltinsX86.inc...
FAILED: tools/clang/include/clang/Basic/BuiltinsX86.inc /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/include/clang/Basic/BuiltinsX86.inc 
cd /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1 && /home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/bin/clang-tblgen -gen-clang-builtins -I /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/clang/include/clang/Basic -I/home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/clang/include -I/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/tools/clang/include -I/home/tcwg-buildbot/worker/clang-aarch64-quick/stage1/include -I/home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/llvm/include /home/tcwg-buildbot/worker/clang-aarch64-quick/llvm/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/tcwg-buildbot/worker/clang-aarch64-quick/llvm/clang/include/clang/Basic/BuiltinsX86.td:147:7: error: Unexpected header name
  def _m_prefetch : X86LibBuiltin<"void(void *)">;
      ^
[4/174] Building CXX object tools/llvm-config/CMakeFiles/llvm-config.dir/llvm-config.cpp.o
[5/174] Generating VCSRevision.h
ninja: build stopped: subcommand failed.

```

</details>

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