[build] Use AS_CASE m4 macro, instead of AS_IF
[build] Use AS_CASE m4 macro, instead of AS_IF

GNOME/json-glib,ebassi/json-glib,oerdnj/json-glib,Distrotech/json-glib,brauliobo/json-glib,ebassi/json-glib,oerdnj/json-glib,oerdnj/json-glib,brauliobo/json-glib,ebassi/json-glib,robtaylor/json-glib-gvariant,Distrotech/json-glib,GNOME/json-glib,Distrotech/json-glib,frida/json-glib,robtaylor/json-glib-gvariant,frida/json-glib,oerdnj/json-glib,brauliobo/json-glib