Include sys/libkern.h for the kernel prototypes of these libkern functions

instead of including the userland string.h header.

Prompted by:	breakage with old string.h from recent machine/types.h fix
Approved by:	peter (in principle)

sys/libkern/bcmp.c

@@ -33,7 +33,7 @@
  * $FreeBSD$
  */
 
-#include <string.h>
+#include <sys/libkern.h>
 #include <machine/endian.h>
 
 typedef	const void	*cvp;

sys/libkern/ffs.c

@@ -33,7 +33,7 @@
  * $FreeBSD$
  */
 
-#include <string.h>
+#include <sys/libkern.h>
 
 /*
  * ffs -- vax ffs instruction

sys/libkern/strcat.c

@@ -33,7 +33,7 @@
  * $FreeBSD$
  */
 
-#include <string.h>
+#include <sys/libkern.h>
 
 char *
 strcat(s, append)

sys/libkern/strcmp.c

@@ -36,7 +36,7 @@
  * $FreeBSD$
  */
 
-#include <string.h>
+#include <sys/libkern.h>
 
 /*
  * Compare strings.

sys/libkern/strcpy.c

@@ -33,7 +33,7 @@
  * $FreeBSD$
  */
 
-#include <string.h>
+#include <sys/libkern.h>
 
 char *
 strcpy(to, from)

sys/libkern/strlen.c

@@ -33,7 +33,7 @@
  * $FreeBSD$
  */
 
-#include <string.h>
+#include <sys/libkern.h>
 
 size_t
 strlen(str)

sys/libkern/strncmp.c

@@ -33,7 +33,7 @@
  * $FreeBSD$
  */
 
-#include <string.h>
+#include <sys/libkern.h>
 
 int
 strncmp(s1, s2, n)

sys/libkern/strncpy.c

@@ -36,7 +36,7 @@
  * $FreeBSD$
  */
 
-#include <string.h>
+#include <sys/libkern.h>
 
 /*
  * Copy src to dst, truncating or null-padding to always copy n bytes.