add gcc version check for -Wno-error=class-memaccess compile option

CMakeLists.txt

@@ -198,9 +198,12 @@ if(GLOW_USE_OWN_GLM)
         GLM_FORCE_CTOR_INIT # 0.9.9 breaks a lot otherwise
     )
     if (GCC)
-        target_compile_options(glm INTERFACE
-            -Wno-error=class-memaccess # new-ish warning that triggers a lot in glm
-        )
+        # class-memaccess error not available before gcc 8
+        if(NOT ${CMAKE_CXX_COMPILER_VERSION} VERSION_LESS 8)
+            target_compile_options(glm INTERFACE
+                -Wno-error=class-memaccess # new-ish warning that triggers a lot in glm
+                )
+        endif()
     endif()
     target_link_libraries(glow PUBLIC glm)
 endif()