[llvm] [utils][UpdateLLCTestChecks] Add MIR support to update_llc_test_checks.py. (PR #164965)

[Valery Pykhtin via llvm-commits]

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@@ -16,6 +16,7 @@
 import sys
 
 from UpdateTestChecks import common
+import update_mir_test_checks  # Reuse MIR parsing code.
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vpykhtin wrote:

I decided to separate the move into a separate [commit ](https://github.com/llvm/llvm-project/pull/140296) and rebase this PR on top of it.

https://github.com/llvm/llvm-project/pull/164965