[llvm] [X86] combineGatherScatter - use FoldConstantArithmetic for truncation of constant build vectors (PR #136033)

[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/14683

<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
0.825 [60/18/1] Linking CXX executable tools/clang/unittests/Basic/BasicTests
0.888 [59/18/2] Linking CXX executable tools/clang/unittests/Parse/ParseTests
1.662 [58/18/3] Linking CXX executable tools/clang/unittests/Format/FormatTests
5.670 [57/18/4] Linking CXX executable tools/clang/unittests/Lex/LexTests
6.152 [56/18/5] Linking CXX executable tools/clang/unittests/libclang/libclangTests
10.206 [55/18/6] Linking CXX executable tools/clang/unittests/Analysis/ClangAnalysisTests
10.615 [54/18/7] Linking CXX executable tools/clang/unittests/AST/ByteCode/InterpTests
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=1211.386719

```

</details>

https://github.com/llvm/llvm-project/pull/136033