Symbol 'SysTick_IRQn' could not be resolved
The proper solution, as explained In this FAQ entry is to uncheck "Index unused headers" from the project properties (or workspace preferences) on the C/C++ Build >> Indexer page. This will automatically do exactly what you have done, but in a lot cleaner way as, as soon as you need one of th eexcluded files it will again be indexed.
Bernard (Ac6)