CMake: Rely on llvm_config again for obtaining the list of required

CMake: Rely on llvm_config again for obtaining the list of required
libraries for an executable.

Now LLVMConfig uses a new system for sorting library dependencies, as
the list of dependent libraries for each entry of FinalLibDeps.txt no
longer is topologically sorted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78787 91177308-0d34-0410-b5e6-96231b3b80d8