[llvm] Add DllMain entry point to `libclang.dll` (PR #171465)

[via llvm-commits]

GkvJwa wrote:

> Seems good, can you please change the description and the title?

Could you help me revise this? My English isn't very good.

I also noticed something odd about the clang format in this file; only the format part was used without being checked.
final:
```
+4037
-3996
lines changed
```

Of course, modifying only a part is also possible; only affecting the format will result in a failure.


https://github.com/llvm/llvm-project/pull/171465