Add support for pthread_attr_get/setguardsize()

* Added the aforementioned functions.
* create_area_etc() now takes a guard size parameter.
* The thread_info::stack_base/end range now refers to the usable range
  only.

headers/posix/pthread.h

@@ -185,6 +185,10 @@ extern int pthread_attr_getschedparam(const pthread_attr_t *attr,
 extern int pthread_attr_setschedparam(pthread_attr_t *attr,
 	const struct sched_param *param);
 
+extern int pthread_attr_getguardsize(const pthread_attr_t *attr,
+	size_t *guardsize);
+extern int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
+
 #if 0   /* Unimplemented attribute functions: */
 
 /* [TPS] */
@@ -196,11 +200,6 @@ extern int pthread_attr_getschedpolicy(const pthread_attr_t *attr,
 	int *policy);
 extern int pthread_attr_setschedpolicy(pthread_attr_t *attr, int policy);
 
-/* [XSI] */
-extern int pthread_attr_getguardsize(const pthread_attr_t *attr,
-	size_t *guardsize);
-extern int pthread_attr_setguardsize(pthread_attr_t *attr, size_t guardsize);
-
 /* [TSA] */
 extern int pthread_attr_getstackaddr(const pthread_attr_t *attr,
 	void **stackaddr);