[llvm] Reapply [MachO] Move getArchTriple implementation..." with fixes. (PR #161949)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-test-suite` running on `ppc64le-clang-test-suite` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/95/builds/18590

<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
...
PASS: LLVM :: tools/llvm-readobj/ELF/file-header-machine-types.test (102294 of 102304)
PASS: LLVM :: tools/llvm-readobj/ELF/note-core.test (102295 of 102304)
PASS: lit :: shtest-shell.py (102296 of 102304)
PASS: LLVM :: tools/llvm-readobj/ELF/AMDGPU/elf-headers.test (102297 of 102304)
PASS: mlgo-utils :: corpus/extract_ir_script.test (102298 of 102304)
PASS: SanitizerCommon-tsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102299 of 102304)
PASS: SanitizerCommon-ubsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102300 of 102304)
PASS: SanitizerCommon-lsan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102301 of 102304)
PASS: SanitizerCommon-asan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102302 of 102304)
PASS: SanitizerCommon-msan-powerpc64le-Linux :: Linux/signal_segv_handler.cpp (102303 of 102304)
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=4204.585736

```

</details>

https://github.com/llvm/llvm-project/pull/161949