I think gcc-defaults is a bit confused about D and sparc.

debian/rules has:
 * multilib_archs contain sparc.
 * d_archs not containing sparc.
 * d_multilib_archs not contain sparc as a result.

This all looks sane.

The default debian/control has gdc-sparc-linux-gnu. This looks wrong. If
you add the current architecture to HOST_ARCHS_sparc, debian/control
also gains gdc-multilib-sparc-linux-gnu. This also looks wrong.

The way this presently works is not that the control generation
considers the aforementioned variables. Rather, there are awk scripts
discarding excess packages. And these awk scripts do not seem to
correctly handle the sparc case.

Patch attached.

Helmut