[MLIR] Change LIT execution dir to build dir (#3674)

LIT creates "Output" folders for each directory with LIT tests.
Before this change, LIT tests were executed in source directory and
"Output" folders had to be removed manually. Git also showed them as
folders to be potentially tracked. This PR changes LIT execution to
build directory to avoid this problem. Similar approach is used in MLIR.

test/mlir/lit.cfg.py

@@ -24,10 +24,10 @@ config.name = 'nGraph MLIR Compiler'
 config.test_format = lit.formats.ShTest(not llvm_config.use_lit_shell)
 
 # test_source_root: The root path where tests are located.
-config.test_source_root = config.ngraph_mlir_test_dir
+config.test_source_root = config.ngraph_mlir_test_src_dir
 
 # test_exec_root: The root path where tests should be run.
-config.test_exec_root = config.ngraph_mlir_test_dir
+config.test_exec_root = config.ngraph_mlir_test_build_dir
 
 llvm_config.use_default_substitutions()
 

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

@@ -22,7 +22,8 @@ config.mlir_tools_dir = "@MLIR_TOOLS_DIR@"
 config.suffixes = ['.mlir']
 
 config.ngraph_mlir_tools_dir = "@NGRAPH_INSTALL_BIN@"
-config.ngraph_mlir_test_dir = "@NGRAPH_LIT_TEST_SRC_DIR@"
+config.ngraph_mlir_test_src_dir = "@NGRAPH_LIT_TEST_SRC_DIR@"
+config.ngraph_mlir_test_build_dir = "@NGRAPH_LIT_TEST_BUILD_DIR@"
 
 lit.llvm.initialize(lit_config, config)