debug.h: Avoid cyclic include dependency

The "lwip/opt.h" header file includes "lwip/debug.h".  Do not include
"lwip/opt.h" in "lwip/debug.h".  Produce an error if "lwip/debug.h" is
included before "lwip/opt.h".

Author: sebhub

contrib/ports/freertos/sys_arch.c

@@ -31,6 +31,7 @@
  */
 
 /* lwIP includes. */
+#include "lwip/opt.h"
 #include "lwip/debug.h"
 #include "lwip/def.h"
 #include "lwip/sys.h"

contrib/ports/unix/port/netif/fifo.c

@@ -3,6 +3,7 @@
 /* ---------------------------------------------- */
 /* --- fifo 4 unix ------------------------------ */
 /* ---------------------------------------------- */
+#include "lwip/opt.h"
 #include "lwip/err.h"
 #include "netif/fifo.h"
 #include "lwip/debug.h"

contrib/ports/unix/port/netif/pcapif.c

@@ -32,6 +32,7 @@
 
 #ifndef linux  /* Apparently, this doesn't work under Linux. */
 
+#include "lwip/opt.h"
 #include "lwip/debug.h"
 
 #include <fcntl.h>

contrib/ports/unix/port/netif/sio.c

@@ -17,6 +17,7 @@
 
 #include "netif/sio.h"
 #include "netif/fifo.h"
+#include "lwip/opt.h"
 #include "lwip/debug.h"
 #include "lwip/def.h"
 #include "lwip/sys.h"

contrib/ports/unix/port/sys_arch.c

@@ -46,6 +46,7 @@
  */
 #define _GNU_SOURCE /* pull in pthread_setname_np() on Linux */
 
+#include "lwip/opt.h"
 #include "lwip/debug.h"
 
 #include <string.h>
@@ -64,7 +65,6 @@
 #endif
 
 #include "lwip/sys.h"
-#include "lwip/opt.h"
 #include "lwip/stats.h"
 #include "lwip/tcpip.h"
 

src/include/lwip/debug.h

@@ -38,7 +38,10 @@
 #define LWIP_HDR_DEBUG_H
 
 #include "lwip/arch.h"
-#include "lwip/opt.h"
+
+#ifndef LWIP_HDR_OPT_H
+#error "lwip/opt.h must be included before this header file"
+#endif
 
 /**
  * @defgroup debugging_levels LWIP_DBG_MIN_LEVEL and LWIP_DBG_TYPES_ON values