For this bug and the mouse one, could you try compiling from
upstream repository to see whether it fails too?
cvs -d :pserver:anonymous@cvs.savannah.gnu.org:/cvsroot/hurd co -r gnumach-1-branch gnumach
In case it fails too, could you try checking out older CVS revisions, so
as to find which commit brought the bug? (there are not so many so that
shouldn't be so long)
In case upstream doesn't fail, could you try dropping debian patches
until you find which one is culprit? (the main suspect would be
20_mmx_support.patch).