Only two of the *rand48.c files need <math.h>, so just #include it in them

src/lib/libc/stdlib/drand48.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: drand48.c,v 1.6 2015/08/27 04:33:31 guenther Exp $ */
+/*	$OpenBSD: drand48.c,v 1.7 2015/09/14 13:30:17 guenther Exp $ */
 /*
  * Copyright (c) 1993 Martin Birgmeier
  * All rights reserved.
@@ -12,6 +12,7 @@
  * to anyone/anything when using this software.
  */
 
+#include <math.h>
 #include "rand48.h"
 
 double

src/lib/libc/stdlib/erand48.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: erand48.c,v 1.4 2015/09/13 08:31:47 guenther Exp $ */
+/*	$OpenBSD: erand48.c,v 1.5 2015/09/14 13:30:17 guenther Exp $ */
 /*
  * Copyright (c) 1993 Martin Birgmeier
  * All rights reserved.
@@ -12,6 +12,7 @@
  * to anyone/anything when using this software.
  */
 
+#include <math.h>
 #include "rand48.h"
 
 double

src/lib/libc/stdlib/rand48.h

@@ -10,13 +10,12 @@
  * of any kind. I shall in no event be liable for anything that happens
  * to anyone/anything when using this software.
  *
- *	$OpenBSD: rand48.h,v 1.5 2015/08/27 04:33:31 guenther Exp $
+ *	$OpenBSD: rand48.h,v 1.6 2015/09/14 13:30:17 guenther Exp $
  */
 
 #ifndef _RAND48_H_
 #define _RAND48_H_
 
-#include <math.h>
 #include <stdlib.h>
 
 __BEGIN_HIDDEN_DECLS