I compiled Python using gcc 4.3.0 with the -Wstrict-overflow, and that's
the only warning I got:  

Objects/doubledigits.c: In function ‘_PyFloat_Digits’:
Objects/doubledigits.c:313: error: assuming signed overflow does not
occur when assuming that (X + c) < X is always false

I am sure yet how to interpret it, though. It says that the overflow
check is in _PyFloat_Digits(), line 313 is in the function add_big(). It
probably means that add_big() gets inlined. I tried to set
-finline-limit=0, but strangely the overflow warning disappears...

I will try to investigate this further, when I will have a bit more time
in my hands.