[Build] build fomantic only if needed

[6543]

as fomantic got seperated (make task) it should also check if something changed and only recompile if needed

[6543]

@silverwind @techknowlogick ... sory missed this on #9945

all in all it's better to make things more atomic :)

[silverwind]

try latest master. 8ca0730 might have solved it for you.

[6543]

@silverwind o missed that - thanks :)