Allow Matplotlib to use system qhull >= 7.2.0

My system has qhull 8.0.0 installed.  Because Matplotlib
doesn't know about my system qhull it builds its own version.
This can cause runtime issues with Matplotlib trying to call
the wrong qhull library.  For example, this fixes the error that

./sage -tp 8 --long --warn-long 31.1 --random-seed=0 src/sage/plot/plot3d/list_plot3d.py

produces

QH6249 qh_lib_check: Incorrect qhull library called.  Size of qhT for caller is 2896, but for library is 2792.
QH6256 qh_lib_check: Cannot continue.  Library 'qhull 7.2.0 (2015.2 2016/01/18)' uses a static qhT (e.g., libqhull.so)

if the system has qhull 8.0.0 installed.

Author: zlscherr

build/pkgs/matplotlib/make-setup-config.py

@@ -1,4 +1,5 @@
 from configparser import ConfigParser
+import pkgconfig
 import os
 
 config = ConfigParser()
@@ -8,6 +9,8 @@
 
 config.add_section('libs')
 config.set('libs', 'system_freetype', 'True')
+if pkgconfig.installed('qhull', '>= 7.2.0'):
+    config.set('libs', 'system_qhull', 'True')
 # lto is problematic if we mix libraries from the OS with our own libraries,
 # which are not necessarily compiled with the same gcc version
 # https://trac.sagemath.org/ticket/27754