we need to override compiler flags in lib/voronoi/Install.py

The default compiler flags in voro++'s config.mk file do not include
-fPIC, which makes it incompatible with building the shared object for
the python wrapper.

lib/voronoi/Install.py

@@ -116,7 +116,7 @@ if buildflag:
 
 if buildflag:
   print("Building Voro++ ...")
-  cmd = 'cd "%s"; make' % homedir
+  cmd = 'cd "%s"; make CXX=g++ CFLAGS="-fPIC -O3"' % homedir
   txt = subprocess.check_output(cmd,stderr=subprocess.STDOUT,shell=True)
   print(txt.decode('UTF-8'))