https://www.yoctoproject.org/downloads
Look at http://downloads.yoctoproject.org/releases/yocto/yocto-1.7.3/poky-dizzy-12.0.3.tar.bz2
It has bitbake recipes for 4.9. You could try putting these in the toolchain layer:
meta-openembedded/toolchain-layer/recipes-devtools/gcc
Sorry I can’t be of more help.
Maybe later.