[llvm] [SandboxIR][NFC] Delete SandboxIR.h (PR #110309)

[Farzon Lotfi via llvm-commits]

farzonl wrote:

Not sure what you changed between the Revert and the ReApply. but things are building now. I am seeing the following warnings though:

```
D:\project\llvm-project\llvm\include\llvm/SandboxIR/Value.h(139,16): warning: unqualified friend declaration referring to type outside of the nearest enclosing namespace is a Microsoft extension; add a nested name specifier [-Wmicrosoft-unqualified-friend]
  139 |   friend class CmpInst;               // For getting `Val`.
      |                ^
      |                ::llvm::
1 warning generated.
[32/3645] Building CXX object lib\Transforms\Vectorize\CMa...LVMVectorize.dir\SandboxVectorizer\DependencyGraph.cpp.obj
In file included from D:\project\llvm-project\llvm\lib\Transforms\Vectorize\SandboxVectorizer\DependencyGraph.cpp:9:
In file included from D:\project\llvm-project\llvm\include\llvm/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.h:27:
In file included from D:\project\llvm-project\llvm\include\llvm/SandboxIR/Instruction.h:15:
In file included from D:\project\llvm-project\llvm\include\llvm/SandboxIR/BasicBlock.h:13:
D:\project\llvm-project\llvm\include\llvm/SandboxIR/Value.h(139,16): warning: unqualified friend declaration referring to type outside of the nearest enclosing namespace is a Microsoft extension; add a nested name specifier [-Wmicrosoft-unqualified-friend]
  139 |   friend class CmpInst;               // For getting `Val`.
      |                ^
      |                ::llvm::
1 warning generated.
[34/3645] Building CXX object lib\Transforms\Vectorize\CMa...Vectorize.dir\SandboxVectorizer\Passes\BottomUpVec.cpp.obj
In file included from D:\project\llvm-project\llvm\lib\Transforms\Vectorize\SandboxVectorizer\Passes\BottomUpVec.cpp:9:
In file included from D:\project\llvm-project\llvm\include\llvm/Transforms/Vectorize/SandboxVectorizer/Passes/BottomUpVec.h:16:
In file included from D:\project\llvm-project\llvm\include\llvm/SandboxIR/Constant.h:20:
In file included from D:\project\llvm-project\llvm\include\llvm/SandboxIR/Argument.h:13:
D:\project\llvm-project\llvm\include\llvm/SandboxIR/Value.h(139,16): warning: unqualified friend declaration referring to type outside of the nearest enclosing namespace is a Microsoft extension; add a nested name specifier [-Wmicrosoft-unqualified-friend]
  139 |   friend class CmpInst;               // For getting `Val`.
      |                ^
      |                ::llvm::
1 warning generated.
```

The platform is Windows 11. The compiler is clang-cl

cmake is setup like so:
```bash
>cmake -G Ninja -B ..\release-llvm-build -S .\llvm\ -DLLVM_ENABLE_PROJECTS="llvm;clang" -DCMAKE_C_COMPILER=clang-cl.exe -DCMAKE_CXX_COMPILER=clang-cl.exe -DCMAKE_BUILD_TYPE=Release
```

https://github.com/llvm/llvm-project/pull/110309