git cannot be cross built from source, because its Build-Depends are not
cross satisfiable. Instead of looking into such a difficult problem, I
looked for easily droppable dependencies. Given that git is normally
reproducible, one can easily verify that a nocheck build with the
following dependencies turned into Build-Conflicts exactly reproduces a
regular build if one keeps debian/changelog unmodified:

 * subversion
 * libsvn-perl
 * libyaml-perl
 * libhttp-date-perl
 * libcgi-pm-perl
 * liberror-perl
 * libmailtools-perl
 * cvs
 * cvsps
 * libdbd-sqlite3-perl
 * unzip
 * libio-pty-perl

It could be that some of these really are unused, but that's difficult
to tell without deeper git knowledge. The safe bet is annotating them
<!nocheck>. Please consider applying the attached patch.

Helmut