setmalloctag in strdup to put allocation at caller

Reference: /n/atom/patch/applied2013/strdupmaltag
Date: Wed Jun 19 06:07:09 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/libc/port/strdup.c	Wed Jun 19 06:06:58 2013
+++ /sys/src/libc/port/strdup.c	Wed Jun 19 06:06:58 2013
@@ -9,6 +9,7 @@
 	ns = malloc(strlen(s) + 1);
 	if(ns == 0)
 		return 0;
+	setmalloctag(ns, getcallerpc(&s));
 
 	return strcpy(ns, s);
 }