[llvm] XCOFF associated metadata (PR #159096)

[Wael Yehia via llvm-commits]

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+; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff < %s | FileCheck %s
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w2yehia wrote:

if this MD is to apply to functions and ifuncs, then will need tests for functions now, and I can add ifuncs tests as part of my ifuncs PR.

Note: When working on the ifunc PR I encountered an issue (that I'm yet to fix) with -fno-functions-sections -fintegrated-as when emiting `.ref` from inside functions. The issue was that relocations in the object file were not generated in increasing address order.

https://github.com/llvm/llvm-project/pull/159096