GUIWindowSystemInfo optimization

for best results, this depend on #3114, GUILabelControl optimization.
with this, and VSING = always, finally i see 'system info' on my RPI working on 50-60%CPU and on 700MHz. my low powered laptop with windows version definitely relaxes too. I didn't dig why this lowers fps in this combination, but i am happy for now.

NOTE: although this will make a lot of users happy, it only optimizes this window, not entire GUI. 

if i found more free time, i will continue with this initiative. any help will be greatly appreciated.