[clang] [lld] [llvm] [ARM] Fix invalid target triples in tests (PR #213588)

[Chris Copeland via cfe-commits]

chrisnc wrote:

I found the first of these while working on extending #111334 to be calling-convention-aware and not just ABI-aware, which was affecting `fp16-fusedMAC.ll` unexpectedly, which it shouldn't have. Turns out it was using `thumbv8.1-m-none-eabi` as the target triple, which is accepted but converts to effectively: arch = thumbv4t, vendor = m, rather than what was intended: `thumbv8.1m.main-none-eabi`. As it happens there are many other examples of mistyped triples in the tests.

[Short godbolt example showing that `thumv8.1-m-none-eabi` is not a valid way to specify the v8 architecture (missing `ldaex`).](https://godbolt.org/z/GocqvWWYx)

https://github.com/llvm/llvm-project/pull/213588