Fix FindLLVM.cmake to use llvm-config (LLVM_CONFIG_EXEC) to set clang, clang++ binary paths
Fix FindLLVM.cmake to use llvm-config (LLVM_CONFIG_EXEC) to set clang, clang++ binary paths

FrozenCaribou/hilti,FrozenCaribou/hilti,FrozenCaribou/hilti,FrozenCaribou/hilti,FrozenCaribou/hilti