As Tobias indicated, the preferred way is to build clang and LLVM in one shot with -DLLVM_ENABLE_PROJECTS=clang.
What happens with your cmake invocation for clang is that it is likely picking up an installed version of LLVM which is outdated.
You could point it to the LLVM you just built with other CMake arguments: it is a supported configuration, see here: RFC: Stand-alone build support