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

[Abhina Sree via cfe-commits]

abhina-sree wrote:

> @abhina-sree do you plan to modify embed in this PR?

Actually Sean has pointed out that if we pass in non-ascii inputs, the tests do in fact fail. So I will look into passing the IsText parameter in the necessary functions. Thanks for pointing this out!

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