chore(shell/CMakeLists): copy mpir.dll when building with MSVC
chore(shell/CMakeLists): copy mpir.dll when building with MSVC

Also simplify code a bit

digama0/lean,leanprover/lean,digama0/lean,dselsam/lean,Kha/lean,digama0/lean,leanprover/lean,fpvandoorn/lean,fpvandoorn/lean,fpvandoorn/lean,fpvandoorn/lean,leanprover/lean,dselsam/lean,leanprover-community/lean,leodemoura/lean,leodemoura/lean,dselsam/lean,leanprover/lean,Kha/lean,dselsam/lean,leodemoura/lean,leanprover-community/lean,Kha/lean,fpvandoorn/lean,digama0/lean,leanprover-community/lean,leanprover-community/lean,leanprover-community/lean,fpvandoorn/lean,Kha/lean,dselsam/lean,leanprover/lean,leodemoura/lean,leanprover-community/lean,Kha/lean,leodemoura/lean,dselsam/lean,digama0/lean,Kha/lean,digama0/lean,leodemoura/lean,leanprover/lean