bpo-32217: Correct usage of ABI tags in freeze. (GH-4719)

Check for sys.abiflags before using since not all platforms have it defined.
diff --git a/Tools/freeze/freeze.py b/Tools/freeze/freeze.py
index 08d09e7..3ab56fd 100755
--- a/Tools/freeze/freeze.py
+++ b/Tools/freeze/freeze.py
@@ -217,7 +217,10 @@
 
     # locations derived from options
     version = '%d.%d' % sys.version_info[:2]
-    flagged_version = version + sys.abiflags
+    if hasattr(sys, 'abiflags'):
+        flagged_version = version + sys.abiflags
+    else:
+        flagged_version = version
     if win:
         extensions_c = 'frozen_extensions.c'
     if ishome: