Add support for building libraries with debugging information in them.

Enable by setting DEBUGLIBS=yes in /etc/mk.conf, then -g libraries will get
installed in /usr/lib/debug.  This directory will be searched first if
gcc is given the -g flag during the link stage.

src/etc/mtree/4.4BSD.dist

@@ -1,4 +1,4 @@
-#	$OpenBSD: 4.4BSD.dist,v 1.90 2000/05/02 10:18:23 niklas Exp $
+#	$OpenBSD: 4.4BSD.dist,v 1.91 2000/05/15 06:10:20 niklas Exp $
 
 /set type=dir uname=root gname=wheel mode=0755
 # .
@@ -250,6 +250,11 @@ xml		gname=bin uname=root mode=0755
 # ./usr/lib/apache
 ..
 
+# ./usr/lib/debug
+debug		gname=bin uname=root mode=0755
+# ./usr/lib/debug
+..
+
 # ./usr/lib
 ..