build failed

- follow the steps within README, get the following error:
```
CMake Error at llvm-project/build/install/lib/cmake/llvm/AddLLVM.cmake:515 (add_dependencies):
The dependency target "MLIRStandard" of target "obj.sair_test_passes" does
not exist.
Call Stack (most recent call first):
llvm-project/build/install/lib/cmake/mlir/AddMLIR.cmake:184 (llvm_add_library)
test/CMakeLists.txt:43 (add_mlir_library)

CMake Error at llvm-project/build/install/lib/cmake/llvm/AddLLVM.cmake:515 (add_dependencies):
The dependency target "MLIRSCFToStandard" of target "obj.sair_lowering"
does not exist.
Call Stack (most recent call first):
llvm-project/build/install/lib/cmake/mlir/AddMLIR.cmake:184 (llvm_add_library)
transforms/CMakeLists.txt:63 (add_mlir_library)

CMake Error at llvm-project/build/install/lib/cmake/llvm/AddLLVM.cmake:515 (add_dependencies):
The dependency target "MLIRStandard" of target "obj.sair_lowering" does not
exist.
Call Stack (most recent call first):
llvm-project/build/install/lib/cmake/mlir/AddMLIR.cmake:184 (llvm_add_library)
transforms/CMakeLists.txt:63 (add_mlir_library)

CMake Error at llvm-project/build/install/lib/cmake/llvm/AddLLVM.cmake:515 (add_dependencies):
The dependency target "MLIRStandardToLLVM" of target "obj.sair_lowering"
does not exist.
Call Stack (most recent call first):
llvm-project/build/install/lib/cmake/mlir/AddMLIR.cmake:184 (llvm_add_library)
transforms/CMakeLists.txt:63 (add_mlir_library)

CMake Error at llvm-project/build/install/lib/cmake/llvm/AddLLVM.cmake:515 (add_dependencies):
The dependency target "MLIRStandard" of target "obj.sair_from_linalg" does
not exist.
Call Stack (most recent call first):
llvm-project/build/install/lib/cmake/mlir/AddMLIR.cmake:184 (llvm_add_library)
transforms/CMakeLists.txt:21 (add_mlir_library)

-- Generating done
CMake Generate step failed. Build files cannot be regenerated correctly.
```
- project commit id : 0998feecd08db4a49f34974f2b881a8937a17eb7
- OS: ubuntu 18.04