MAC: mac.h: Fix missing includes/typedefs

This fixes inclusion from userspace, and also kernel inclusion for
source files not including explicitly nor implicitly <sys/types.h>.

Reviewed by:    jamie
Approved by:    markj (mentor)
MFC after:      5 days
Sponsored by:   The FreeBSD Foundation
Differential Revision:  https://reviews.freebsd.org/D46896

(cherry picked from commit 5140ccf2268b0e771c89e46f46c60e1fee7637c3)

sys/sys/mac.h

@@ -47,6 +47,13 @@
 #ifndef _SYS_MAC_H_
 #define	_SYS_MAC_H_
 
+#include <sys/_types.h>
+
+#ifndef _SIZE_T_DECLARED
+typedef	__size_t	size_t;
+#define	_SIZE_T_DECLARED
+#endif
+
 #ifndef _POSIX_MAC
 #define	_POSIX_MAC
 #endif
@@ -72,6 +79,13 @@ typedef struct mac	*mac_t;
 
 #ifndef _KERNEL
 
+#include <sys/cdefs.h> /* For __BEGIN_DECLS and __END_DECLS. */
+
+#ifndef _PID_T_DECLARED
+typedef	__pid_t		pid_t;		/* process id */
+#define	_PID_T_DECLARED
+#endif
+
 /*
  * Location of the userland MAC framework configuration file.  mac.conf
  * set defaults for MAC-aware applications.