[llvm] [NFC][StructurizeCFG] Add a test that can crash StructurizeCFG pass (PR #126087)

[via llvm-commits]

Prabhuk wrote:

This test fails in our (Fuchsia) toolchain CI linux host builders. I am currently investigating this.

```
XPASS: LLVM :: Transforms/StructurizeCFG/simple-structurizecfg-crash.ll (50157 of 58077)
******************** TEST 'LLVM :: Transforms/StructurizeCFG/simple-structurizecfg-crash.ll' FAILED ********************
Exit Code: 0

Command Output (stdout):
--
; ModuleID = '/b/s/w/ir/x/w/llvm-llvm-project/llvm/test/Transforms/StructurizeCFG/simple-structurizecfg-crash.ll'
source_filename = "/b/s/w/ir/x/w/llvm-llvm-project/llvm/test/Transforms/StructurizeCFG/simple-structurizecfg-crash.ll"

define void @foo() {
entry:
  br label %cond.false

cond.true:                                        ; preds = %cond.false
  br label %cond.end

cond.false:                                       ; preds = %entry
  br i1 true, label %cond.true, label %cond.end

cond.end:                                         ; preds = %cond.true, %cond.false
  ret void
}

--
Command Output (stderr):
--
RUN: at line 1: /b/s/w/ir/x/w/llvm_build/bin/opt -S -passes=structurizecfg /b/s/w/ir/x/w/llvm-llvm-project/llvm/test/Transforms/StructurizeCFG/simple-structurizecfg-crash.ll -o -
+ /b/s/w/ir/x/w/llvm_build/bin/opt -S -passes=structurizecfg /b/s/w/ir/x/w/llvm-llvm-project/llvm/test/Transforms/StructurizeCFG/simple-structurizecfg-crash.ll -o -
```

Link to the logs: https://logs.chromium.org/logs/fuchsia/buildbucket/cr-buildbucket/8723305309974990577/+/u/clang/tests/stdout
Link to the bot: https://luci-milo.appspot.com/ui/p/fuchsia/builders/toolchain.ci/clang-host-linux-x64/b8723305798791238737/overview

https://github.com/llvm/llvm-project/pull/126087