#437: use compiler detections to guard pragmas to suppress excessive warnings

Author: nauhygon

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/cpp/CppGenerator.java

@@ -372,7 +372,7 @@ private static CharSequence generateGroupProperty(
             indent + "#pragma clang diagnostic ignored \"-Wtautological-compare\"\n" +
             indent + "#endif\n" +
             indent + "        return m_actingVersion >= %1$sSinceVersion();\n" +
-            indent + "#if SBE_SBE_CLANG\n" +
+            indent + "#if defined(__clang__)\n" +
             indent + "#pragma clang diagnostic pop\n" +
             indent + "#endif\n" +
             indent + "    }\n",