Set ABI, DEFAULT_ABI and friends consistently with other profiles.
Stable on alpha, bug #497490

(Portage version: 2.2.10/cvs/Linux x86_64, signed Manifest commit with key CE5D54E8)
Set CHOST_${ABI} for consistence.
Set CHOST_o32 for consistence.
CXXFLAGS=-O2 should be safe.