[llvm] [llvm][CMake] Fix llvm shared library when using ninja multi config (PR #65451)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> I'm not really an expert on this. @MaskRay perhaps?

I am not familiar with CMake... but this patch does address a problem.

I suggest that you add to the description the following instruction and also some description from #63800.

```
% cmake -G 'Ninja Multi-Config' -Sllvm -B/tmp/out/ninja-multi -DCMAKE_CONFIGURATION_TYPES='Debug;Release' -DLLVM_LINK_LLVM_DYLIB=on -DLLVM_TARGETS_TO_BUILD=host
% ninja -C /tmp/out/ninja-multi -f build-Debug.ninja llvm-mc
...
ld.lld: error: cannot find version script /tmp/out/ninja-multi/Debug/lib/tools/llvm-shlib/simple_version_script.map
```

https://github.com/llvm/llvm-project/pull/65451