[llvm] Add metadata pointer regex substitution to MIR update script (PR #163253)

[Joe Nash via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 6
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Sisyph wrote:

Since the test requires amdgpu, probably should have the test name prefixed with 'amdgpu'. But I don't see a reason this script should only work on amdgpu. Maybe other backends don't emit raw pointers in the MIR?

https://github.com/llvm/llvm-project/pull/163253