All gcc ebuilds starting from gcc-4.6.4-r2 (ones that have been funtooized and not using toolchain.eclass anymore) are totally incapable of crosscompiling. They are both missing --target directive and CTARGET is set to CHOST in pkg_setup(). This either needs to be work-arounded by backporting some parts of toolchain.eclass or guarded by big fat warning when CTARGET != CHOST is detected, that this version just could not cross-compile.

Older ebuilds, such as 4.6.2-r1 and 4.3.3-r2 have no such problem as they are using toolchain.eclass.