[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 `openmp-s390x-linux` running on `systemz-1` while building `clang` at step 5 "compile-openmp".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/88/builds/7575

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

```
Step 5 (compile-openmp) failure: build (failure)
...
236.783 [1885/4/3391] Building AttrHasAttributeImpl.inc...
236.789 [1884/4/3392] Building CXX11AttributeInfo.inc...
236.799 [1883/4/3393] Building BuiltinsBPF.inc...
236.801 [1882/4/3394] Building Builtins.inc...
236.822 [1881/4/3395] Building BuiltinsNVPTX.inc...
236.824 [1880/4/3396] Building BuiltinsHexagon.inc...
236.833 [1879/4/3397] Building BuiltinsSPIRV.inc...
236.835 [1878/4/3398] Building BuiltinsRISCV.inc...
236.848 [1877/4/3399] Building BuiltinsX86_64.inc...
236.855 [1876/4/3400] Building BuiltinsX86.inc...
FAILED: tools/clang/include/clang/Basic/BuiltinsX86.inc /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/tools/clang/include/clang/Basic/BuiltinsX86.inc 
cd /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build && /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/bin/clang-tblgen -gen-clang-builtins -I /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/clang/include/clang/Basic -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/clang/include -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/tools/clang/include -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.build/include -I/home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/llvm/include /home/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/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/uweigand/sandbox/buildbot/openmp-s390x-linux/llvm.src/clang/include/clang/Basic/BuiltinsX86.td:147:7: error: Unexpected header name
  def _m_prefetch : X86LibBuiltin<"void(void *)">;
      ^
236.892 [1876/3/3401] Building arm_neon.inc...
244.985 [1876/2/3402] Linking CXX shared library lib/libLTO.so.21.0git
245.434 [1876/1/3403] Linking CXX executable bin/llvm-lto
ninja: build stopped: subcommand failed.

```

</details>

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