Add unusedFunction to suppression list

As cppcheck does not consider an override, despite the fact Qt framework
will call into this

buildconfig/CMake/CppCheck_Suppressions.txt.in

@@ -11,6 +11,10 @@ noExplicitConstructor
 // Hide warnings about shadowed members for inheritance. Typically "m_log" with Algorithm
 duplInheritedMember
 
+// Hide unused functions, cppcheck does not consider headers, so many Qt overrides
+// called by Qt will be marked as unused
+unusedFunction
+
 // We have some potentially uninitialized member vars but too many to fix at the moment
 uninitMemberVar