Enable torch-mlir LIT tests in Bazel (#1585)

Adds support to run `.mlir` LIT tests in bazel. 

```
bazel test @torch-mlir//test/...
```

Follow-on PR will contain these updates:
- Add tests to GHA CI workflow
- Add `.py` LIT tests to bazel

test/lit.cfg.py

@@ -63,7 +63,7 @@ llvm_config.with_environment('PATH', config.llvm_tools_dir, append_path=True)
 if "Windows" in config.host_os:
   config.python_executable = '"%s"' % (config.python_executable)
 
-tool_dirs = [config.standalone_tools_dir, config.llvm_tools_dir]
+tool_dirs = [config.standalone_tools_dir, config.llvm_tools_dir, config.torch_mlir_obj_root]
 tools = [
     'torch-mlir-opt',
     ToolSubst('%PYTHON', config.python_executable, unresolved='ignore'),

utils/bazel/torch-mlir-overlay/test/BUILD.bazel

@@ -0,0 +1,42 @@
+# This file is licensed under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+load("@bazel_skylib//rules:expand_template.bzl", "expand_template")
+load("@llvm-project//llvm:lit_test.bzl", "lit_test", "package_path")
+
+package(
+    default_visibility = [
+        "//visibility:public",
+    ],
+)
+
+expand_template(
+    name = "lit_site_cfg_py",
+    testonly = True,
+    out = "lit.site.cfg.py",
+    substitutions = {
+        "@LIT_SITE_CFG_IN_HEADER@": "# Autogenerated, do not edit.",
+        "@TORCH_MLIR_SOURCE_DIR@": package_path("@torch-mlir//:BUILD"),
+        "\"@TORCH_MLIR_BINARY_DIR@\"": "os.path.join(os.environ['TEST_SRCDIR'], 'torch-mlir')",
+        "\"@LLVM_TOOLS_DIR@\"": "os.path.join(os.environ['TEST_SRCDIR'], 'llvm-project', 'llvm')",
+        # All disabled, but required to substituted because they are not in quotes.
+        "@MLIR_ENABLE_BINDINGS_PYTHON@": "0",
+        "@TORCH_MLIR_ENABLE_JIT_IR_IMPORTER@": "0",
+        "@TORCH_MLIR_ENABLE_MHLO@": "0",
+    },
+    template = "lit.site.cfg.py.in",
+)
+
+# Common data used by most lit tests.
+filegroup(
+    name = "lit_data",
+    testonly = True,
+    data = [
+        "lit.cfg.py",
+        "lit.site.cfg.py",
+        "@llvm-project//llvm:FileCheck",
+        "@llvm-project//llvm:count",
+        "@llvm-project//llvm:not",
+    ],
+)

utils/bazel/torch-mlir-overlay/test/Conversion/BUILD.bazel

@@ -0,0 +1,15 @@
+load("@llvm-project//llvm:lit_test.bzl", "lit_test")
+
+package(default_visibility = ["//visibility:public"])
+
+[
+    lit_test(
+        name = "%s.test" % src,
+        srcs = [src],
+        data = [
+            "@torch-mlir//:torch-mlir-opt",
+            "@torch-mlir//test:lit_data",
+        ],
+    )
+    for src in glob(["**/*.mlir"])
+]

utils/bazel/torch-mlir-overlay/test/Dialect/BUILD.bazel

@@ -0,0 +1,15 @@
+load("@llvm-project//llvm:lit_test.bzl", "lit_test")
+
+package(default_visibility = ["//visibility:public"])
+
+[
+    lit_test(
+        name = "%s.test" % src,
+        srcs = [src],
+        data = [
+            "@torch-mlir//:torch-mlir-opt",
+            "@torch-mlir//test:lit_data",
+        ],
+    )
+    for src in glob(["**/*.mlir"])
+]

utils/bazel/torch-mlir-overlay/test/RefBackend/BUILD.bazel

@@ -0,0 +1,15 @@
+load("@llvm-project//llvm:lit_test.bzl", "lit_test")
+
+package(default_visibility = ["//visibility:public"])
+
+[
+    lit_test(
+        name = "%s.test" % src,
+        srcs = [src],
+        data = [
+            "@torch-mlir//:torch-mlir-opt",
+            "@torch-mlir//test:lit_data",
+        ],
+    )
+    for src in glob(["**/*.mlir"])
+]