[llvm] [AMDGPU][StructurizeCFG] pre-commit tests: maintain branch_weights metadata (PR #109812)

[Matt Arsenault via llvm-commits]

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@@ -0,0 +1,72 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -mtriple=amdgcn-- -S -structurizecfg %s | FileCheck -check-prefix=OPT %s
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arsenm wrote:

```suggestion
; RUN: opt -S -mtriple=amdgcn-- -passes=structurizecfg %s | FileCheck -check-prefix=OPT %s
```

This belongs in test/Transform/StructurizeCFG, and should use new PM 

https://github.com/llvm/llvm-project/pull/109812