On my system, emerging gnome-base/librsvg with ABI 64 only is successful, but multilib with ABI 64 and 32 causes the abi_x86_32 portion to fail with an unresolved external in libcairo.so for glBlendFuncSeparate.
This function is actually in libGL.so.1 and editing the Makefile to include "-lGL" in the list of libraries allowed emerge to complete (using "keepwork" FEATURES to use the result of my patch and successful build).
I presume that pkg-config or a similar mechanism should have caused libGL to be included in the link command automatically, but this did not happen.
I had already re-emerged the dependencies, and particularly including mesa and cairo.
Unfortunately I can't paste the output from emerge --info because the clipboard is temporarily not available on the virtual machine where I experienced the failure (X is currently functional but not KDE 5 or any other proper window manager)
gtk+ encounters the same problem (undefined reference to glBuildFuncSeparate, fixed by adding -lGL to Makefile in several subdirectories, everywhere that -lcairo appears)
Are you referring to x32 or the normal x86_32 support? Anyway, please provide the full build.log and emerge --info output