Refactor (MASConstraintMaker): Fix to remove Xcode warning.

Split declaration and assignment of anyAttribute variable to remove Xcode warning.
I'd use `__unused` attribute:

`__unused MASAttribute anyAttribute = MASAttributeLeft | MASAttributeRight | MASAttributeTop | MASAttributeBottom | MASAttributeLeading | MASAttributeTrailing | MASAttributeWidth | MASAttributeHeight | MASAttributeCenterX | MASAttributeCenterY | MASAttributeBaseline;`