Add new uses ninja[:verbose]

This allows to use the ninja build system.
USES= cmake ninja
Will make cmake generate ninja files and use ninja.

Mk/Uses/ninja.mk

@@ -0,0 +1,30 @@
+# $FreeBSD$
+#
+# Provide support to use ninja
+#
+# MAINTAINER: portmgr@FreeBSD.org
+#
+# Feature:	ninja
+# Usage:	USES=ninja[:verbose]
+
+.if !defined(_INCLUDE_USES_NINJA_MK)
+_INCLUDE_USES_NINJA_MK=	yes
+
+.if defined(ninja_ARGS)
+.if ${ninja_ARGS} == verbose
+MAKE_ARGS+=	-v
+.else
+IGNORE=	Incorrect aruments for 'USES+= ninja:${ninja_ARGS}' valid argument is 'verbose'
+.endif
+.endif
+
+BUILD_DEPENDS=	ninja:${PORTSDIR}/devel/ninja
+
+CMAKE_ARGS+=	-GNinja
+MAKEFILE=
+MAKE_CMD=	ninja
+MAKE_FLAGS=
+MAKE_ENV=	${DESTDIRNAME}=${STAGEDIR}
+_DESTDIR_VIA_ENV=	yes
+
+.endif