sys: Add files to Doxygen group

Canonicalize brief descriptions.

Update #3707.

cpukit/doxygen/top-level-groups.h

@@ -40,6 +40,14 @@
  *   RTEMS.
  */
 
+/**
+ * @defgroup RTEMSAPISystemLibrary System Library
+ *
+ * @ingroup RTEMSAPI
+ *
+ * @brief This group contains the system library APIs of RTEMS.
+ */
+
 /**
  * @defgroup RTEMSDeviceDrivers Device Drivers
  *

cpukit/include/sys/endian.h

@@ -1,3 +1,12 @@
+/**
+ * @file
+ *
+ * @ingroup RTEMSAPISystemLibrary
+ *
+ * @brief This header file provides interfaces of the system endianness
+ *   support.
+ */
+
 /*-
  * Copyright (c) 2002 Thomas Moestl <tmm@FreeBSD.org>
  * All rights reserved.

cpukit/include/sys/priority.h

@@ -1,3 +1,11 @@
+/**
+ * @file
+ *
+ * @ingroup RTEMSAPISystemLibrary
+ *
+ * @brief This header file provides interfaces of the process priority support.
+ */
+
 /*-
  * SPDX-License-Identifier: BSD-4-Clause
  *

cpukit/include/sys/statvfs.h

@@ -3,10 +3,11 @@
 /**
  * @file
  *
- * @brief Interface to the statvfs() Set of API Methods
+ * @ingroup RTEMSAPISystemLibrary
  *
- * This include file defines the interface to the statvfs() set of
- * API methods. The statvfs as defined by the SUS:
+ * @brief This header file provides the statvfs() and fstatvfs() interfaces.
+ *
+ * The statvfs() is defined by the SUS:
  *
  * - http://www.opengroup.org/onlinepubs/009695399/basedefs/sys/statvfs.h.html
  */