add patch to VORONOI package external build so it will compile with BSD make

  ExternalProject_Add(voro_build

    URL https://download.lammps.org/thirdparty/voro++-0.4.6.tar.gz

    URL_MD5 2338b824c3b7b25590e18e8df5d68af9

    CONFIGURE_COMMAND "" BUILD_COMMAND make ${VORO_BUILD_OPTIONS} BUILD_IN_SOURCE 1 INSTALL_COMMAND ""

    PATCH_COMMAND patch -b -p0 < ${LAMMPS_LIB_SOURCE_DIR}/voronoi/voro-make.patch

    CONFIGURE_COMMAND ""

    BUILD_COMMAND make ${VORO_BUILD_OPTIONS}

    BUILD_IN_SOURCE 1

    INSTALL_COMMAND ""

    BUILD_BYPRODUCTS <SOURCE_DIR>/src/libvoro++.a

    )

  ExternalProject_get_property(voro_build SOURCE_DIR)

--- src/Makefile.orig	2020-05-03 03:50:23.501557199 -0400

+++ src/Makefile	2020-05-03 03:53:32.147681674 -0400

@@ -10,10 +10,10 @@

 # List of the common source files

 objs=cell.o common.o container.o unitcell.o v_compute.o c_loops.o \

      v_base.o wall.o pre_container.o container_prd.o

-src=$(patsubst %.o,%.cc,$(objs))

+src=$(objs:.o=.cc)

 # Makefile rules

-all: libvoro++.a voro++

+all: depend libvoro++.a voro++

 depend:

 	$(CXX) -MM $(src) >Makefile.dep

@@ -22,12 +22,12 @@

 libvoro++.a: $(objs)

 	rm -f libvoro++.a

-	ar rs libvoro++.a $^

+	$(AR) rs libvoro++.a $(objs)

 voro++: libvoro++.a cmd_line.cc

 	$(CXX) $(CFLAGS) -L. -o voro++ cmd_line.cc -lvoro++

-%.o: %.cc

+.cc.o:

 	$(CXX) $(CFLAGS) -c $<

 help: Doxyfile $(SOURCE)