Fix llvm_ir_correct tests on Windows

[tdusnoki]

On Windows some tests are unable to open iso_fortran_env.mod unless we include it explicitly.

related issue: #1363

[bryanpkc]

%flags is for specifying custom options, and typically undefined. You need to find another way to solve this problem. Why can't the compiler locate iso_fortran_env.mod? It should be in the include/ directory of the Classic Flang installation, which should be one of the standard include paths.

[kaadam]

%flags is for specifying custom options, and typically undefined. You need to find another way to solve this problem. Why can't the compiler locate iso_fortran_env.mod? It should be in the include/ directory of the Classic Flang installation, which should be one of the standard include paths.

Yes, you're right. The 'AddFlangSystemIncludeArgs' implementation is missed from MSVC toolchain, please see: flang-compiler/classic-flang-llvm-project#161

[tdusnoki]

After testing with flang-compiler/classic-flang-llvm-project/pull/161 this PR is no longer necessary, thanks for the feedback.