configure: tune optimisation flags for PowerPC/Darwin again
configure: tune optimisation flags for PowerPC/Darwin again

Last night's run with slimmed down -fast flags ran again slower, so go
back to the original flags, dropping what should be already included.
This ends up in just -O3.  Hopefully tomorrow we'll be back at the speed
of rev 39707.

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb