If not icon file is specified use the default Python Applet icons.
Fixes 719303.
diff --git a/Lib/plat-mac/buildtools.py b/Lib/plat-mac/buildtools.py
index 6e6396d..bebab19 100644
--- a/Lib/plat-mac/buildtools.py
+++ b/Lib/plat-mac/buildtools.py
@@ -289,6 +289,10 @@
                 icnsname = None
         else:
             plistname = None
+    if not icnsname:
+        dft_icnsname = os.path.join(sys.prefix, 'Resources/Python.app/Contents/Resources/PythonApplet.icns')
+        if os.path.exists(dft_icnsname):
+            icnsname = dft_icnsname
     if not os.path.exists(rsrcname):
         rsrcname = None
     if progress: