Issue #17845: Clarify the message setup.py prints upon successfully
building Python but having some optional module which didn't build.

Patch by Yogesh Chaudhari.
diff --git a/setup.py b/setup.py
index 798220b..b2417c7 100644
--- a/setup.py
+++ b/setup.py
@@ -259,8 +259,9 @@
 
         if missing:
             print()
-            print("Python build finished, but the necessary bits to build "
-                   "these modules were not found:")
+            print("Python build finished successfully!")
+            print("The necessary bits to build these optional modules were not "
+                  "found:")
             print_three_column(missing)
             print("To find the necessary bits, look in setup.py in"
                   " detect_modules() for the module's name.")