Set system-independent default compiler to use C++ 11

Ensure compatibility with post 3.5 versions of protobuf out of the box.
Note that nothing in OSI per see requires C++ 11, so users catering to
older platforms using older protobuf releases can switch this back if
needed using the normal CMake configuration mechanisms.

Signed-off-by: Carsten Drösser <carsten.droesser@gmail.com>

Author: carstendroesser

CMakeLists.txt

@@ -2,6 +2,9 @@ cmake_minimum_required(VERSION 3.5)
 
 project(open_simulation_interface)
 
+# set default compiler
+set(CMAKE_CXX_STANDARD 11)
+
 # Set a default build type if none was specified
 set(default_build_type "Release")
 if(EXISTS "${CMAKE_SOURCE_DIR}/.git")