[llvm-diff] Diff attributes & metadata

[aapanfilovv]

Added diffing function, param, return attrs, metadata attach

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[DavidSpickett]

That Buildkite failure will be fixed if you update your branch to be based on the latest changes from the main branch. It's not anything to do with your changes.

[kazutakahirata]

@aapanfilovv Would you consider adding tests for your changes? It might be cumbersome to add as many tests as the number of if (Complain), but maybe you could add tests for some representative test cases!? Grep for llvm-diff under llvm/test for examples. Some of them create differences with cat and sed.

[aapanfilovv]

@kazutakahirata Done, ping.

[kazutakahirata]

LGTM modulo a minor comment about the line ending.