Adds cpp test for Halide IR cse pass.

tests/cpp/ir_cse_pass_test.cc

+#include <dmlc/logging.h>
+#include <gtest/gtest.h>
+#include <tvm/tvm.h>
+#include <pass/CSE.h>
+
+TEST(IR_PASS, CSE) {
+  using namespace Halide::Internal;
+  cse_test();
+}
+
+int main(int argc, char ** argv) {
+  testing::InitGoogleTest(&argc, argv);
+  testing::FLAGS_gtest_death_test_style = "threadsafe";
+  return RUN_ALL_TESTS();
+}