Issue #16537: Check whether self.extensions is empty in setup.py.

Patch by Jonathan Hosmer.
diff --git a/Misc/ACKS b/Misc/ACKS
index ccfc18e..c86acd9 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -582,6 +582,7 @@
 Nadav Horesh
 Alon Horev
 Jan Hosang
+Jonathan Hosmer
 Alan Hourihane
 Ken Howard
 Brad Howes
diff --git a/Misc/NEWS b/Misc/NEWS
index 2ad73fd..b50f45d 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -205,6 +205,9 @@
 Build
 -----
 
+- Issue #16537: Check whether self.extensions is empty in setup.py. Patch by
+  Jonathan Hosmer.
+
 - The documentation Makefile no longer automatically downloads Sphinx. Users are
   now required to have Sphinx already installed to build the documentation.