Comment 2 for bug 1863116

Let me provide some more background on this (getting some lines back from the initial bug description):

On an (as of today) updated focal installation (on s390x) I needed to install the crossbuild-essential-amd64 package, but it's not installable and it seems to be the same for all "crossbuild-essential-*" packages. It's btw. the same on Eoan, too.

Now, I ran into this because I want to do a kernel test compile with a modified kernel option. If one modifies a kernel option, "fakeroot debian/rules updateconfigs" needs to be called.
I was told by the kernel team that at some point in time (somewhere between bionic and eoan) CROSS_COMPILE setting became needed to address architecture-dependent tests in Kconfig options. Hence cross toolchains are now required.
At least amd64 is needed, I don't know yet if more is needed (but I assume it's more).

Right now - as workaround - I need to do the kernel config changes on my local amd64 workstation run updateconfigs and can then proceed with build and test on the s390x target platform.

But it must be possible to prepare and compile a kernel with a modified kernel option on a single target platform.