[SystemZ][z/OS] Add IsText Argument to GetFile and GetFileOrSTDIN

Add the `IsText` argument to `GetFile` and `GetFileOrSTDIN` which will help z/OS distinguish between text and binary correctly. This is an extension to [this patch](https://reviews.llvm.org/D97785)

Reviewed By: abhina.sreeskantharajan, amccarth

Differential Revision: https://reviews.llvm.org/D100488

GitOrigin-RevId: e71994a239d5f807c1c75515bfa512495224469f
8 files changed