Optimize gtk_css_node_declaration_has_class
Optimize gtk_css_node_declaration_has_class

This function is getting called a lot. Statistics for the gtk3-demo
listbox example show most calls with 0-4 classes. Unrolling the cases
a bit brings the instruction count in callgrind from 93M to 52M.

jigpu/gtk,alexlarsson/gtk,jadahl/gtk,davidgumberg/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,jadahl/gtk,jadahl/gtk,jigpu/gtk,davidgumberg/gtk,jadahl/gtk,grubersjoe/adwaita,grubersjoe/adwaita,grubersjoe/adwaita,jadahl/gtk,alexlarsson/gtk,davidgumberg/gtk,jigpu/gtk,grubersjoe/adwaita,jigpu/gtk,jigpu/gtk,davidgumberg/gtk,davidgumberg/gtk,alexlarsson/gtk,davidgumberg/gtk,alexlarsson/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,davidgumberg/gtk,grubersjoe/adwaita,grubersjoe/adwaita,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,grubersjoe/adwaita,jadahl/gtk,alexlarsson/gtk,jigpu/gtk