Fix strdup conflict on other platforms

In the FreeBSD kernel the strdup signature is:

```
char	*strdup(const char *__restrict, struct malloc_type *);
```

It's unfortunate that the developers have chosen to change
the signature of libc functions - but it's what I have to
deal with.

Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #9433

module/os/linux/spl/spl-kmem.c

@@ -120,18 +120,18 @@ __strdup(const char *str, int flags)
 }
 
 char *
-strdup(const char *str)
+kmem_strdup(const char *str)
 {
 	return (__strdup(str, KM_SLEEP));
 }
-EXPORT_SYMBOL(strdup);
+EXPORT_SYMBOL(kmem_strdup);
 
 void
-strfree(char *str)
+kmem_strfree(char *str)
 {
 	kfree(str);
 }
-EXPORT_SYMBOL(strfree);
+EXPORT_SYMBOL(kmem_strfree);
 
 /*
  * General purpose unified implementation of kmem_alloc(). It is an

module/os/linux/spl/spl-kstat.c

@@ -631,7 +631,7 @@ kstat_detect_collision(kstat_proc_entry_t *kpep)
 	parent = kmem_asprintf("%s", kpep->kpe_module);
 
 	if ((cp = strrchr(parent, '/')) == NULL) {
-		strfree(parent);
+		kmem_strfree(parent);
 		return (0);
 	}
 
@@ -639,13 +639,13 @@ kstat_detect_collision(kstat_proc_entry_t *kpep)
 	if ((module = kstat_find_module(parent)) != NULL) {
 		list_for_each_entry(tmp, &module->ksm_kstat_list, kpe_list) {
 			if (strncmp(tmp->kpe_name, cp+1, KSTAT_STRLEN) == 0) {
-				strfree(parent);
+				kmem_strfree(parent);
 				return (EEXIST);
 			}
 		}
 	}
 
-	strfree(parent);
+	kmem_strfree(parent);
 	return (0);
 }
 

module/os/linux/spl/spl-taskq.c

@@ -1038,7 +1038,7 @@ taskq_create(const char *name, int nthreads, pri_t pri,
 	spin_lock_init(&tq->tq_lock);
 	INIT_LIST_HEAD(&tq->tq_thread_list);
 	INIT_LIST_HEAD(&tq->tq_active_list);
-	tq->tq_name = strdup(name);
+	tq->tq_name = kmem_strdup(name);
 	tq->tq_nactive = 0;
 	tq->tq_nthreads = 0;
 	tq->tq_nspawn = 0;
@@ -1178,7 +1178,7 @@ taskq_destroy(taskq_t *tq)
 
 	spin_unlock_irqrestore(&tq->tq_lock, flags);
 
-	strfree(tq->tq_name);
+	kmem_strfree(tq->tq_name);
 	kmem_free(tq, sizeof (taskq_t));
 }
 EXPORT_SYMBOL(taskq_destroy);