Drop the need for dpkg-architecture, we only build for linux.
Thanks to Károly Kasza for catching this one.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>

diff -Nura ifupdown.orig/defn2c.pl ifupdown/defn2c.pl
--- ifupdown.orig/defn2c.pl	2014-11-18 16:39:28.878772655 -0300
+++ ifupdown/defn2c.pl	2014-11-18 16:43:41.120456676 -0300
@@ -2,7 +2,7 @@
 
 use strict;
 
-my $DEB_HOST_ARCH_OS = `dpkg-architecture -qDEB_HOST_ARCH_OS`;
+my $DEB_HOST_ARCH_OS = "linux";
 
 $DEB_HOST_ARCH_OS =~ s/\n//;