d/control-in: allow build-dep on non-x86 to ignore build-indep
Due to most roms now being cross-built Build-Indep contains plenty
of build dependencies for cross toolchains. Due to that on non-x86 one
can no more apt build-dep things for a native build as that does not
skip the Build-Depends-Indep.
gcc-s390x-linux-gnu | 4:10.2.1-1 | testing | amd64, arm64, i386, ppc64el gcc-alpha-linux-gnu | 4:10.2.1-1 | testing | amd64, i386 gcc-powerpc64-linux-gnu | 4:10.2.1-1 | testing | amd64, i386 gcc-sparc64-linux-gnu | 4:10.2.1-1 | testing | amd64, i386 gcc-hppa-linux-gnu | 4:10.2.1-1 | testing | amd64, i386 gcc-riscv64-linux-gnu | 4:10.2.1-1 | testing | amd64, arm64, i386, ppc64el
Those tools only exists on a few architectures, marking it as needed
for only those allows that apt build-dep works on non-x86 while the actual
build on e.g. an ftp upload isn't changing at all.