> There is a lot of value in being able to compile with -Wstrict-overflow 
> and know that every warning omitted is something to be looked at.

I agree in principle; this certainly applies to -Wall.  But -Wstrict-
overflow doesn't do a particularly good job of finding signed overflow
cases:  there are a good few false positives, and it doesn't pick up
the many cases of actual everyday signed overflow e.g., in unicode_hash, 
byteshash, set_lookkey, etc.), so it doesn't seem a particular good basis 
for code rewriting.