Update to C++17 (#742)

Signed-off-by: Chris Lalancette <[email protected]>

Author: clalancette

test_launch_testing/CMakeLists.txt

@@ -6,8 +6,10 @@ if(NOT CMAKE_C_STANDARD)
   set(CMAKE_C_STANDARD 99)
 endif()
 
+# Default to C++17
 if(NOT CMAKE_CXX_STANDARD)
-  set(CMAKE_CXX_STANDARD 14)
+  set(CMAKE_CXX_STANDARD 17)
+  set(CMAKE_CXX_STANDARD_REQUIRED ON)
 endif()
 
 if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")