In preparation for removal of groff from base add USES=groff

it will handle the dependencies on groff by using groff from ports if not
available in base

Reviewed by:	swills
Approved by:	swills
Differential Revision:	https://reviews.freebsd.org/D9084

Mk/Uses/groff.mk

@@ -0,0 +1,31 @@
+# $FreeBSD$
+#
+# handle dependency on groff
+#
+# Feature:	groff
+# Usage:	USES=groff
+# Valid ARGS:	build (default, implicit), run, both
+
+.if !defined(_INCLUDE_USES_GROFF_MK)
+_INCLUDE_USES_GROFF_MK=	yes
+
+.  if !exists(/usr/bin/groff)
+.    if empty(groff_ARGS)
+groff_ARGS=	build
+.    endif
+
+_GROFF_DEPENDS=	groff:textproc/groff
+
+.    if ${groff_ARGS} == "build"
+BUILD_DEPENDS+=	${_GROFF_DEPENDS}
+.    elif ${groff_ARGS} == "run"
+RUN_DEPENDS+=	${_GROFF_DEPENDS}
+.    elif ${groff_ARGS} == "both"
+BUILD_DEPENDS+=	${_GROFF_DEPENDS}
+RUN_DEPENDS+=	${_GROFF_DEPENDS}
+.    else
+IGNORE=	USES=groff - invalid args: [${groff_ARGS}] specified
+.    endif
+.  endif
+
+.endif