configure.py: make check for PyQt5.sip module non-fatal

python2 fails to load this if PyQt5 is not available, so...
bootstrapping fail. Since this is only really required at
runtime anyway, make the check itself informative only.

PyQt5_gpl-5.11.2-sip_check.patch

@@ -0,0 +1,21 @@
+diff -up PyQt5_gpl-5.11.2/configure.py.sip_check PyQt5_gpl-5.11.2/configure.py
+--- PyQt5_gpl-5.11.2/configure.py.sip_check	2018-07-11 14:10:21.751437714 -0500
++++ PyQt5_gpl-5.11.2/configure.py	2018-07-11 14:12:13.035482279 -0500
+@@ -647,7 +647,7 @@ class TargetConfiguration:
+         try:
+             from PyQt5 import sip
+         except ImportError:
+-            error(
++            inform(
+                     "Unable to import PyQt5.sip.  Make sure you have "
+                     "configured SIP to create a private copy of the sip "
+                     "module.")
+@@ -2919,7 +2919,7 @@ def check_sip(target_config):
+     try:
+         from PyQt5 import sip
+     except ImportError:
+-        error(
++        inform(
+                 "Unable to import PyQt5.sip.  Make sure you have configured "
+                 "SIP to create a private copy of the sip module.")
+