the downloaded fireware works.
In next step I download a linux tarbal from https://developer.arm.com/open-source/gnu-toolchain/gnu-rm/downloads , unpacked and set PATH so this is used during compilation.
And it works. So issue is probably with some missing option of Gentoo crossdev compiled arm gcc. I’ll will investigate it and let you know if I found a working setup. If not, I can use the downloaded toolchain.