Add linker warnings for rand() and random() and various related functions.

ok deraadt@

src/lib/libc/stdlib/rand.c

@@ -39,14 +39,29 @@ rand_r(u_int *seed)
 	return (*seed % ((u_int)RAND_MAX + 1));
 }
 
+#if defined(APIWARN)
+__warn_references(rand_r,
+    "warning: rand_r() isn't random; consider using arc4random()");
+#endif
+
 int
 rand(void)
 {
 	return (rand_r(&next));
 }
 
+#if defined(APIWARN)
+__warn_references(rand,
+    "warning: rand() isn't random; consider using arc4random()");
+#endif
+
 void
 srand(u_int seed)
 {
 	next = seed;
 }
+
+#if defined(APIWARN)
+__warn_references(srand,
+    "warning: srand() seed choices are invariably poor");
+#endif

src/lib/libc/stdlib/random.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: random.c,v 1.18 2013/03/15 19:07:53 tedu Exp $ */
+/*	$OpenBSD: random.c,v 1.19 2013/08/01 19:42:08 kettenis Exp $ */
 /*
  * Copyright (c) 1983 Regents of the University of California.
  * All rights reserved.
@@ -233,6 +233,11 @@ srandom(unsigned int x)
 	UNLOCK();
 }
 
+#if defined(APIWARN)
+__warn_references(srandom,
+    "warning: srandom() seed choices are invariably poor");
+#endif
+
 /*
  * srandomdev:
  *
@@ -267,6 +272,11 @@ srandomdev(void)
 	UNLOCK();
 }
 
+#if defined(APIWARN)
+__warn_references(srandomdev,
+    "warning: srandomdev() usage; consider switching to arc4random()");
+#endif
+
 /*
  * initstate:
  *
@@ -429,3 +439,8 @@ random(void)
 	UNLOCK();
 	return r;
 }
+
+#if defined(APIWARN)
+__warn_references(random,
+    "warning: random() isn't random; consider using arc4random()");
+#endif