[clang] [llvm] [SystemZ][z/OS] Add new openFileForReadBinary function, and pass IsText parameter to getBufferForFile (PR #111723)

[kadir çetinkaya via cfe-commits]

https://github.com/kadircet requested changes to this pull request.

thanks! I think this LG at a high-level, added some comments about the details.

I think it'd be worthwhile to add some tests (even if not now, probably going forward). as otherwise such rare use cases might regress quite frequently.

https://github.com/llvm/llvm-project/pull/111723