[llvm] [llvm-lib] [Object] Use ECSYMBOLS section for ARM64EC importlib symbols. (PR #68328)

[Martin Storsjö via llvm-commits]

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

The code changes look consistent and reasonable to me, so that's good.

For the test, I'm not entirely sure exactly which aspects of the test output would have been different without this change though.

https://github.com/llvm/llvm-project/pull/68328