[clang] [CMake] Fix variable name (PR #127967)

[Madhur Amilkanthwar via cfe-commits]

madhur13490 wrote:

> > The fix is NOT correct. You need to enclose in quotes as @tstellar mentions in #126876
> 
> ` llvm_canonicalize_cmake_booleans` converts the string to an integer so you don't need the quotes now that this function is called with the correct variable. This is what the generated file looks like now:
> 
> ```
> config.use_llvm_build = 1
> ```

Oh.. I see. Thanks!

https://github.com/llvm/llvm-project/pull/127967