cad/freecad: chase mpich/openmpi dependency switch after ed69f586

FreeCAD must match it's vtk

cad/freecad/Makefile

 PORTNAME=	FreeCAD
 DISTVERSION=	0.20.1
-PORTREVISION=	1
+PORTREVISION=	2
 # use these for bugfixes/snapshots
 # DISTVERSION=	0.18-16093 # git rev-list --count
 # DISTVERSIONSUFFIX=	-g690774c0e
@@ -29,14 +29,14 @@ LIB_DEPENDS=	libexpat.so:textproc/expat2 \
 		libboost_thread.so:devel/boost-libs \
 		libarea.so:devel/libarea \
 		libmed.so:french/med \
-		libmpi.so:net/mpich \
 		libshiboken2.cpython-${PYTHON_SUFFIX}${PYTHON_ABIVER}.so:devel/shiboken2@${PY_FLAVOR} \
 		libhdf5-110.so:science/hdf5-110
+
 RUN_DEPENDS=	${PYTHON_PKGNAMEPREFIX}pivy>0:graphics/py-pivy@${PY_FLAVOR} \
 		${PYTHON_SITELIBDIR}/matplotlib/__init__.py:math/py-matplotlib@${PY_FLAVOR}
 
 USES=		dos2unix compiler:c++17-lang cmake cpe gl eigen:3 fortran jpeg \
-		localbase:ldflags pkgconfig python:3.7+ localbase qt:5 xorg
+		localbase:ldflags mpi:openmpi pkgconfig python:3.7+ localbase qt:5 xorg
 USE_GITHUB=	yes
 USE_XORG=	ice sm x11 xext xt
 USE_GL=		gl glu