[llvm] [CMake] Make specifying invalid build type a fatal error (PR #72021)

[Igor Zhukov via llvm-commits]

https://github.com/fsb4000 approved this pull request.

Yes. Looks good. Warnings could be often ignored and we can define LLVM_ADDITIONAL_BUILD_TYPES  if we need custom build type.

https://github.com/llvm/llvm-project/pull/72021