Make tempnam/mktemp deprecated.

Bug: 19340053
Change-Id: Ib02c65814ef97cd1758fd8142b73736cc8bc1700
diff --git a/libc/include/stdlib.h b/libc/include/stdlib.h
index cbd7aeb..84bf56d 100644
--- a/libc/include/stdlib.h
+++ b/libc/include/stdlib.h
@@ -58,7 +58,7 @@
 extern int clearenv(void);
 
 extern char* mkdtemp(char*);
-extern char* mktemp(char*) __warnattr("mktemp possibly used unsafely; consider using mkstemp");
+extern char* mktemp(char*) __attribute__((deprecated("mktemp is unsafe, use mkstemp or tmpfile instead")));
 
 extern int mkostemp64(char*, int);
 extern int mkostemp(char*, int);