[llvm] [GlobalISel] Add G_CONCAT_VECTOR handling in computeNumSignBits (PR #142355)

[Usha Gupta via llvm-commits]

usha1830 wrote:

1 test failed due to timeout. Looks like an intermittent and unrelated issue
```
Timed Out Tests (1):
  lldb-shell :: Settings/TestCxxFrameFormatRecursive.test
```

https://github.com/llvm/llvm-project/pull/142355