abuild: add support for ABUILD_BLACKLIST

The ABUILD_BLACKLIST can be used to give abuild a list of packages that
is known to fail to build. This can be used to reduce build retries
when building many/all packages recursively.

abuild.in

@@ -1588,6 +1588,12 @@ builddeps() {
 		# ignore if dependency is in other repo
 		[ -d "$dir" ] || continue
 
+		# check if dep is blacklisted
+		if list_has $pkg $ABUILD_BLACKLIST; then
+			error "$pkg is blacklisted"
+			return 1
+		fi
+
 		# break circular deps
 		list_has $pkg $ABUILD_VISITED && continue
 		export ABUILD_VISITED="$ABUILD_VISITED $pkg"