CMAKE: add error message if you are trying to build engine with gcc v…

…ersion less then 7.0

CMakeLists.txt

@@ -11,6 +11,12 @@ if(CCACHE_FOUND)
     set_property(GLOBAL PROPERTY RULE_LAUNCH_LINK ccache)
 endif(CCACHE_FOUND)
 
+if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+    if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 7.0)
+        message(FATAL_ERROR "Building with a gcc version less than 7.0 is not supported.")
+    endif()
+endif()
+
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive --std=c++17")
 #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive") This is for the future versions
 #set(CMAKE_CXX_STANDARD 14) #Otherwise adds -std=gnu++11 and breaks successful building