CMake: Make helper function static

Change-Id: If4b0ebd2a40f2250533a717a1b57b0eb7d13ae9a
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>

src/plugins/projectexplorer/kitmanager.cpp

@@ -268,7 +268,7 @@ static bool isLoaded()
     return d->m_initialized;
 }
 
-bool greaterPriority(KitInformation *a, KitInformation *b)
+static bool greaterPriority(KitInformation *a, KitInformation *b)
 {
     return a->priority() > b->priority();
 }