Change SEM_VALUE_MAX (maximum value of a POSIX semaphore) from UINT_MAX

to INT_MAX.  Otherwise, a process could create a semaphore (or increase
its value via ksem_post()) beyond INT_MAX and sem_getvalue() would return
a negative value.  sem_getvalue() is only supposed to return a negative
value if that is the number of waiters for that semaphore.

MFC after:	2 weeks

sys/sys/semaphore.h

@@ -37,12 +37,14 @@
 #ifndef _SEMAPHORE_H_
 #define _SEMAPHORE_H_
 
+#include <machine/_limits.h>
+
 /* Opaque type definition. */
 struct sem;
 typedef	struct sem *	sem_t;
 
 #define	SEM_FAILED	((sem_t *)0)
-#define	SEM_VALUE_MAX	(~0U)		/* Equivalent to UINT_MAX. */
+#define	SEM_VALUE_MAX	__INT_MAX
 
 #ifndef _KERNEL
 #include <sys/cdefs.h>