rL82131 changed -O from -O1 to -O2, because -O1 was not different from
-O2 at that time.
GCC treats -O as -O1 and there is now work to make -O1 meaningful.
We can change -O back to -O1 again.
Actually it was http://llvm.org/r82131 that mapped -O to -O2 (I just refactored it). Originally it seems it was mapped to -O1.
Because this seems to have done quite intentionally, I'm a little vary of changing it back. I'm not sure who would be a good person to have insights here though.