[llvm] [AArch64][Windows] Add llvm-readobj support for ec_context unwind opcode (PR #69515)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo approved this pull request.

The change itself looks good, thanks!

This is lacking a test, but OTOH I don't see a standalone test for disassembling all the other corresponding opcodes either.

Many of them were added in llvm-readobj in the same commit as the MC layer code for assembling them, in f5e2ea9a43221be9576056c4912796cf37331cd7, so the readobj changes are covered by those MC tests at least.

So as long as this is merged close together with #69520 which does provide some test coverage for this, I think it's fine.

https://github.com/llvm/llvm-project/pull/69515