add $CLEANFILES for libraries

Reference: /n/sources/patch/applied/cleanfiles-for-libs
Date: Fri Oct 12 12:11:47 CES 2012
Signed-off-by: steve@quintile.net

--- /sys/src/cmd/mklib	Fri Oct 12 12:08:19 2012
+++ /sys/src/cmd/mklib	Fri Oct 12 12:08:16 2012
@@ -16,6 +16,9 @@
 %.$O:	%.c
 	$CC $CFLAGS $stem.c
 
+%.$O:	%.C
+	c++/$CC $CFLAGS $stem.C
+
 %.$O:	%.s
 	$AS $AFLAGS $stem.s
 
@@ -40,7 +43,7 @@
 	rm -f $LIB
 
 clean:V:
-	rm -f *.[$OS] y.tab.? y.output y.error
+	rm -f *.[$OS] y.tab.? y.output y.error $CLEANFILES
 
 update:V:
 	update $UPDATEFLAGS $UPDATE