Exclude makedev from buildd chroots

It was historically excluded, and apparently breaks some builds (e.g.
mir).

debian/changelog

@@ -1,3 +1,10 @@
+livecd-rootfs (2.408.52) UNRELEASED; urgency=medium
+
+  * Exclude makedev from buildd chroots, since it was historically excluded
+    and apparently breaks some builds (e.g. mir).
+
+ -- Colin Watson <cjwatson@ubuntu.com>  Tue, 17 Sep 2019 13:41:49 +0200
+
 livecd-rootfs (2.408.51) xenial; urgency=medium
 
   * ubuntu-cpc: Only produce explicitly specified artifacts (LP: #1837254)

live-build/auto/config

@@ -626,6 +626,10 @@ case $SUBPROJECT in
 		# likely to involve work both here and in launchpad-buildd.
 		OPTS="${OPTS:+$OPTS }--security false --volatile false"
 
+		# makedev was Priority: required in xenial, but has
+		# historically been excluded from buildd chroots.
+		export LB_BOOTSTRAP_EXCLUDE='makedev'
+
 		add_package install adduser
 		add_package install policyrcd-script-zg2
 		add_package install pkgbinarymangler