[SystemZ][z/OS][Windows] Add new functions that set Text/Binary mode for Stdin and...

[SystemZ][z/OS][Windows] Add new functions that set Text/Binary mode for Stdin and Stdout based on OpenFlags

On Windows, we want to open a file in Binary mode if OF_CRLF bit is not set. On z/OS, we want to open a file in Binary mode if the OF_Text bit is not set.

This patch creates two new functions called ChangeStdinMode and ChangeStdoutMode which will take OpenFlags as an arg to determine which mode to set stdin and stdout to. This will enable patches like https://reviews.llvm.org/D100056 to not affect Windows when setting the OF_Text flag for raw_fd_streams.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D100130