[llvm] [llvm-debuginfo-analyzer] Fix crash with WebAssembly dead code (PR #141616)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-cmake-x86_64-avx512-linux` running on `avx512-intel64` while building `llvm` at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/133/builds/18475

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

```
Step 7 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'LLVM :: tools/llvm-debuginfo-analyzer/WebAssembly/wasm-32bit-tombstone.s' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/llvm-mc -arch=wasm32 -filetype=obj                /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/test/tools/llvm-debuginfo-analyzer/WebAssembly/wasm-32bit-tombstone.s                 -o /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/test/tools/llvm-debuginfo-analyzer/WebAssembly/Output/wasm-32bit-tombstone.s.tmp.wasm-32bit-tombstone.wasm # RUN: at line 27
+ /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/llvm-mc -arch=wasm32 -filetype=obj /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/test/tools/llvm-debuginfo-analyzer/WebAssembly/wasm-32bit-tombstone.s -o /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/test/tools/llvm-debuginfo-analyzer/WebAssembly/Output/wasm-32bit-tombstone.s.tmp.wasm-32bit-tombstone.wasm
/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/llvm-mc: error: invalid target 'wasm32'.
--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/141616