[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:

Failed at `FAIL: BOLT :: RISCV/fake-label-no-entry.c` this time.  I'll give it a day or so and try again.

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