Enable SSA at -O0

[Paolo Bonzini]

> I'd rather do a -Og instead.  -O1 already badly messes with debuggability.
> For -Og I would chose -Os inlining heuristics for example and only do
> basic propagation and dead code removal but no memory optimization or
> things like SRA or IVOPTs.  Just ccp, copyprop, dce and inline accessor style
> things to make C++ usable.

But since in 4.4 there is no more any reason to use -O1 when alias 
analysis blows up, why couldn't -O1 *be* -Og?

Paolo