[Flang][Windows] Backport fixes for CMake + Flang on Windows

[omjavaid]

CMake support for flang MSVC was broken and has been merged recently [1].
CMake 3.28 will have all the latest fixes required for Flang + MSVC combination.

Compiling Fortran OpenBLAS project with llvm-17 and latest CMake still caused issues which were fixed by #66516 which depends on #66270

This issue aims to backport both these PRs to 17.x to have Flang successfully build projects like OpenBLAS which used along MSVC.

[omjavaid]

/cherry-pick a685715

[llvmbot]

@llvm/issue-subscribers-mlir-llvm

Author: Omair Javaid (omjavaid)

CMake support for flang MSVC was broken and has been merged recently [1]. CMake 3.28 will have all the latest fixes required for Flang + MSVC combination.

Compiling Fortran OpenBLAS project with llvm-17 and latest CMake still caused issues which were fixed by #66516 which depends on #66270

This issue aims to backport both these PRs to 17.x to have Flang successfully build projects like OpenBLAS which used along MSVC.

[llvmbot]

/branch llvm/llvm-project-release-prs/issue70458

[omjavaid]

/cherry-pick a685715 5f476b8

[llvmbot]

/pull-request llvm/llvm-project-release-prs#752

[llvmbot]

/branch llvm/llvm-project-release-prs/issue70458