[CMake] Introduce LLVM_RUNTIME_OUTPUT_INTDIR and LLVM_LIBRARY_OUTPUT_INTDIR to reduce references to CMAKE_CFG_INTDIR.

Each of them forms like;
  ${CMAKE_BINARY_DIR}/bin/${CMAKE_CFG_INTDIR}
  ${CMAKE_BINARY_DIR}/lib/${CMAKE_CFG_INTDIR}

llvm-svn: 197394