Use PyQt5 module path to find SIP bindings (#105)

`sipconfig._pkg_config['default_mod_dir']` is currently used to find the PyQt5 SIP bindings, but this location is determined by where SIP is installed, which may not be the same as where PyQt5 is installed. A real world example of this is in Nix, where each package is installed to a separate isolated directory. Instead, we can use `PyQt5.__path__[0]`, which will always point to the location of the PyQt5 module.

Author: lopsided98

cmake/sip_configure.py

@@ -5,6 +5,7 @@
 import subprocess
 import sys
 
+import PyQt5
 from PyQt5 import QtCore
 import sipconfig
 
@@ -62,7 +63,7 @@ def get_sip_dir_flags(config):
         sip_flags = QtCore.PYQT_CONFIGURATION['sip_flags']
 
         # Archlinux installs sip files here by default
-        default_sip_dir = os.path.join(sipconfig._pkg_config['default_mod_dir'], 'PyQt5', 'bindings')
+        default_sip_dir = os.path.join(PyQt5.__path__[0], 'bindings')
         if os.path.exists(default_sip_dir):
             return default_sip_dir, sip_flags