ensure C++14 standard for MacOS compatibility

Author: artcore-c

rmw_test_fixture_implementation/CMakeLists.txt

@@ -1,6 +1,11 @@
 cmake_minimum_required(VERSION 3.5)
 project(rmw_test_fixture_implementation LANGUAGES C CXX)
 
+# Ensure C++14 support
+if(NOT CMAKE_CXX_STANDARD)
+  set(CMAKE_CXX_STANDARD 14)
+endif()
+
 if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
   add_compile_options(-Wall -Wextra -Wpedantic)
 endif()