bpo-39448: Add regen-frozen makefile target. (GH-18174)

Add the "regen-frozen" makefile target that regenerates the code for the
frozen __hello__ module.
diff --git a/Python/frozen_hello.h b/Python/frozen_hello.h
new file mode 100644
index 0000000..9c566cc
--- /dev/null
+++ b/Python/frozen_hello.h
@@ -0,0 +1,13 @@
+/* Generated with Tools/freeze/regen_frozen.py */
+static unsigned char M___hello__[] = {
+    227,0,0,0,0,0,0,0,0,0,0,0,0,
+    0,0,0,0,2,0,0,0,64,0,0,0,115,
+    16,0,0,0,100,0,90,0,101,1,100,1,131,
+    1,1,0,100,2,83,0,41,3,84,122,12,72,
+    101,108,108,111,32,119,111,114,108,100,33,78,41,
+    2,90,11,105,110,105,116,105,97,108,105,122,101,
+    100,218,5,112,114,105,110,116,169,0,114,2,0,
+    0,0,114,2,0,0,0,218,4,110,111,110,101,
+    218,8,60,109,111,100,117,108,101,62,1,0,0,
+    0,115,2,0,0,0,4,1,
+};