tests: add optional GoogleTest-based smoke-tests and CMake support (BUILD_GTEST_SMOKE)

Lts/DDS/DdsUnitTestsPlaceholder/ddsDataTopicTests_gtest.cpp

@@ -0,0 +1,7 @@
+#include <gtest/gtest.h>
+
+TEST(DataTopicSmokeGTest, Format) {
+  char buf[64];
+  snprintf(buf, sizeof(buf), "%d-%s", 42, "abc");
+  EXPECT_STREQ(buf, "42-abc");
+}