[llvm] SimplifyIndVar: teach widenLoopCompare about samesign (PR #125851)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `arc-builder` running on `arc-worker` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/3/builds/11368

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
0.810 [59/18/1] Linking CXX executable tools/clang/unittests/Basic/BasicTests
1.926 [58/18/2] Linking CXX executable tools/clang/unittests/Format/FormatTests
5.782 [57/18/3] Linking CXX executable tools/clang/unittests/Lex/LexTests
6.266 [56/18/4] Linking CXX executable tools/clang/unittests/libclang/libclangTests
9.441 [55/18/5] Linking CXX executable tools/clang/unittests/Rewrite/RewriteTests
11.814 [54/18/6] Linking CXX executable tools/clang/unittests/CrossTU/CrossTUTests
12.476 [53/18/7] Linking CXX executable tools/clang/unittests/libclang/CrashTests/libclangCrashTests
13.306 [52/18/8] Linking CXX executable tools/clang/unittests/Tooling/Syntax/SyntaxTests
14.188 [51/18/9] Linking CXX executable tools/clang/unittests/InstallAPI/InstallAPITests
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1214.943815

```

</details>

https://github.com/llvm/llvm-project/pull/125851