Debuginfod Testing & fixes: 3rd times the charm? (#87676)

I believe I've got the tests properly configured to only run on Linux
x86(_64), as I don't have a Linux AArch64/Arm device to diagnose what's
going wrong with the tests (I suspect there's some issue with generating
`.note.gnu.build-id` sections...)

The actual code fixes have now been reviewed 3 times:
https://github.com/llvm/llvm-project/pull/79181 (moved shell tests to
API tests), https://github.com/llvm/llvm-project/pull/85693 (Changed
some of the testing infra), and
https://github.com/llvm/llvm-project/pull/86812

 (didn't get the tests
configured quite right). The Debuginfod integration for symbol
acquisition in LLDB now works with the `executable` and `debuginfo`
Debuginfod network requests working properly for normal, `objcopy
--only-keep-debug` stripped, split-dwarf, and `objcopy
--only-keep-debug` stripped *plus* split-dwarf symbols/binaries.

The reasons for the multiple attempts have been tests on platforms I
don't have access to (Linux AArch64/Arm + MacOS x86_64). I believe I've
got the tests properly disabled for everything except for Linux x86(_64)
now. I've built & tested on MacOS AArch64 and Linux x86_64.

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Co-authored-by: Kevin Frei <freik@meta.com>