[llvm] [SystemZ][z/OS] Open YAML files for read as text files (PR #121340)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-darwin` running on `doug-worker-3` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/23/builds/6219

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
UNSUPPORTED: mlgo-utils :: corpus/extract_ir_test.py (80736 of 80746)
UNSUPPORTED: mlgo-utils :: corpus/make_corpus_test.py (80737 of 80746)
UNSUPPORTED: mlgo-utils :: pytype.test (80738 of 80746)
PASS: lld :: MachO/x86-64-stubs.s (80739 of 80746)
PASS: lld :: MachO/zippered.yaml (80740 of 80746)
PASS: lld :: MachO/weak-reference.s (80741 of 80746)
PASS: lld :: MinGW/lib.test (80742 of 80746)
PASS: lld :: MachO/weak-definition-direct-fetch.s (80743 of 80746)
PASS: lld :: MinGW/driver.test (80744 of 80746)
PASS: lit :: shtest-define.py (80745 of 80746)
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=2637.489704

```

</details>

https://github.com/llvm/llvm-project/pull/121340