Issue 705836: Fix struct.pack(">f", 1e40) to behave consistently
across platforms:  it should now raise OverflowError on all
platforms.  (Previously it raised OverflowError only on
non IEEE 754 platforms.)

Also fix the (already existing) test for this behaviour
so that it actually raises TestFailed instead of just
referencing it.
diff --git a/Misc/NEWS b/Misc/NEWS
index 65ce4c0..3397f0c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -21,6 +21,10 @@
 Library
 -------
 
+- Issue #705836: struct.pack(">f", x) now raises OverflowError on all
+  platforms when x is too large to fit into an IEEE 754 float; previously
+  it only raised OverflowError on non IEEE 754 platforms.
+
 - Issue #1106316: pdb.post_mortem()'s parameter, "traceback", is now
   optional: it defaults to the traceback of the exception that is currently
   being handled (is mandatory to be in the middle of an exception, otherwise