[llvm-mt] "llvm-mt: error: no libxml2". Why for cross compiling?

https://github.com/llvm/llvm-project/blob/main/llvm/tools/llvm-mt/CMakeLists.txt

Based on this if we do not have libxml2 enabled, even we won't even be able to produce the binary. I do have libxml2 provided but it fails.

```
set(LLVM_ENABLE_LIBXML2 FORCE_ON)
```