we have just added/verified support for 'multilib' recently in our OE builds. this is what I would recommend to use, not the secondary toolchain. The secondary toolchain is more suited for compiling firmware for other cores on the platform (DSP, ..). 'multilib' is an OE feature that lets you mix 32 and 64 bits libraries (and apps) in the same system.
I don't know how you setup your OE builds, which distro you are using, .. if you are using the OE RPB setup and if you are using our morty or master branch, then multilib is enabled by default now.
The main change when we brought up this feature is this commit:
Once you enable multilib you can add a 32 bit lib or apps by adding "lib3-xxx" in your image. E.g. "lib32-htop" will add the htop package built for 32 bit, while the rest of the system is 64 bit.