[C++][Gandiva] Add support for LLVM 23.1

### Describe the enhancement requested

It seems that LLVM 23.1.0 and 23.1.1 have been released:

https://llvm.org/

> LLVM Release Schedule:
>
> 23.1.x
> Tue Jul 14th, 2026: release/23.x branch
> Fri Jul 17th, 2026: 23.1.0-rc1 was released
> Tue Jul 28th, 2026: 23.1.0-rc2 was released
> Tue Aug 12th, 2026: 23.1.0-rc3 was released
> Tue Aug 25th, 2026: 23.1.0 was released
> Tue Sep 8th, 2026: 23.1.1 was released
> Tue Sep 22nd, 2026: 23.1.2
> Tue Oct 6th, 2026: 23.1.3
> Tue Oct 20th, 2026: 23.1.4
> Tue Nov 3rd, 2026: 23.1.5
> Tue Nov 17th, 2026: 23.1.6
> Tue Dec 1st, 2026: 23.1.7
> Tue Dec 15th, 2026: 23.1.8
> Tue Dec 29th, 2026: 23.1.9 (if necessary)

It seems that conda provides LLVM 23.1. So our conda related CI jobs are failing:

https://github.com/ursacomputing/crossbow/actions/runs/34261627141/job/102180729366#step:7:1246

```text
CMake Warning at cmake_modules/FindLLVMAlt.cmake:30 (find_package):
Could not find a configuration file for package "LLVM" that is compatible
with requested version "22.1".

The following configuration files were considered but not accepted:

/opt/conda/envs/arrow/lib/cmake/llvm/LLVMConfig.cmake, version: 23.1.0
The version found is not compatible with the version requested.

Call Stack (most recent call first):
src/gandiva/CMakeLists.txt:39 (find_package)
```

### Component(s)

C++, Gandiva