devel/libgusb: Unbreak build

Register a dependency on py-setuptools. Somewhere in the dependency
chain a hard dep on it probably got dropped.

While here, use OPTIONS helpers, and adjust some build dependencies.
gtk-doc is only needed when DOCS is enabled, and vala is only needed
when VAPI is enabled.

Based on a patch from Matthew Wener.
PR:		270788
Reported by:	Fredrik Eriksson

devel/libgusb/Makefile

@@ -10,9 +10,9 @@ WWW=		https://github.com/hughsie/libgusb
 LICENSE=	LGPL21
 LICENSE_FILE=	${WRKSRC}/COPYING
 
-BUILD_DEPENDS=	gtk-doc>0:textproc/gtk-doc
+BUILD_DEPENDS=	${PYTHON_PKGNAMEPREFIX}setuptools>=0:devel/py-setuptools@${PY_FLAVOR}
 
-USES=		gnome meson pkgconfig vala:build
+USES=		gnome meson pkgconfig python:build
 
 USE_GITHUB=	yes
 GH_ACCOUNT=	hughsie
@@ -23,13 +23,10 @@ OPTIONS_DEFINE=		DOCS VAPI
 OPTIONS_DEFAULT=	DOCS VAPI
 OPTIONS_SUB=		yes
 
-.include <bsd.port.options.mk>
+DOCS_BUILD_DEPENDS=	gtk-doc>0:textproc/gtk-doc
+DOCS_MESON_TRUE=	docs
 
-.if !${PORT_OPTIONS:MDOCS}
-MESON_ARGS+=	-Ddocs=false
-.endif
-.if !${PORT_OPTIONS:MVAPI}
-MESON_ARGS+=	-Dvapi=false
-.endif
+VAPI_MESON_TRUE=	vapi
+VAPI_USES=		vala:build
 
 .include <bsd.port.mk>