[MLIR] Improve lit test config files and tools (#4010)

This PR fixes some of the inconveniences that we had with lit in nGraph
and aligns configuration files with MLIR/LLVM.
In particular:
  - `make install` is not needed to run lit test with the latest
    compiled version of testing tools (ngraph-opt).
  - LD_LIBRARY_PATH doesn't need to be modified.

CMakeLists.txt

@@ -539,6 +539,9 @@ if (NOT NGRAPH_BUILD_DIR)
     endif()
 endif()
 
+# Build destination directory for nGraph binaries and tools.
+set(NGRAPH_BUILD_BIN ${CMAKE_CURRENT_BINARY_DIR}/bin)
+
 set(EXTERNAL_INSTALL_DIR ${CMAKE_BINARY_DIR}/external)
 
 if(NOT DEFINED EXTERNAL_PROJECTS_ROOT)

src/contrib/mlir/tools/ngraph-opt/CMakeLists.txt

@@ -28,4 +28,9 @@ add_executable(ngraph-opt
 
 target_link_libraries(ngraph-opt PRIVATE ${LIBS})
 
+set_target_properties(ngraph-opt PROPERTIES
+                      RUNTIME_OUTPUT_DIRECTORY_DEBUG ${NGRAPH_BUILD_BIN}
+                      RUNTIME_OUTPUT_DIRECTORY_RELEASE ${NGRAPH_BUILD_BIN}
+)
+
 install(TARGETS ngraph-opt RUNTIME DESTINATION ${NGRAPH_INSTALL_BIN})

test/mlir/lit.cfg.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #*****************************************************************************
+"""Lit runner configuration."""
 
 import lit.formats
 from lit.llvm import llvm_config

test/mlir/lit.site.cfg.py.in

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #*****************************************************************************
+"""Lit runner site configuration."""
 
 import lit.llvm
 
@@ -21,7 +22,7 @@ config.mlir_obj_root = "@MLIR_BUILD_DIR@"
 config.mlir_tools_dir = "@MLIR_TOOLS_DIR@"
 config.suffixes = ['.mlir']
 
-config.ngraph_mlir_tools_dir = "@CMAKE_INSTALL_PREFIX@/@NGRAPH_INSTALL_BIN@"
+config.ngraph_mlir_tools_dir = "@NGRAPH_BUILD_BIN@"
 config.ngraph_mlir_test_src_dir = "@NGRAPH_LIT_TEST_SRC_DIR@"
 config.ngraph_mlir_test_build_dir = "@NGRAPH_LIT_TEST_BUILD_DIR@"