[clang] [llvm] [z/OS] treat text files as text files so auto-conversion is done (PR #90128)

[Sean Perry via cfe-commits]

perry-ca wrote:

> LGTM, but check why the following test in checks failed: `FAIL: BOLT :: RISCV/unnamed-sym-no-entry.c`

Looks unrelated.   I'm kicking off another build.

https://github.com/llvm/llvm-project/pull/90128