Simplify LWIP build

* Make copy of `lwip/contrib/ports/unix/lib/` in `Linux` ($UNAME) directory, rather than attempting to patch it

lwipopts.h

* Put simplified lwipopts.h into root directory, but don't #include directly - it's added via lwip/opts.h
* Add default DNS server
* Add debug flags

Testing with `SystemClock_NTP` sample with DNS/UDP debugging enabled shows UDP requests are being sent out but no responses received. Further investigation required.

Sming/Arch/Host/Components/hostlib/host_lwip.cpp

@@ -21,7 +21,6 @@
 #include "hostlib.h"
 
 extern "C" {
-#include "lwipopts.h"
 #include <lwip/init.h>
 #include <lwip/ip_addr.h>
 #include <lwip/timeouts.h>

Sming/Arch/Host/Components/lwip/Linux/CMakeLists.txt

@@ -0,0 +1,33 @@
+cmake_minimum_required(VERSION 3.8)
+
+project(lwip C)
+
+set (BUILD_SHARED_LIBS OFF)
+
+if (NOT CMAKE_SYSTEM_NAME STREQUAL "Linux" AND NOT CMAKE_SYSTEM_NAME STREQUAL "GNU")
+    message(FATAL_ERROR "Lwip shared library is only working on Linux or the Hurd")
+endif()
+
+set(LWIP_DIR ${CMAKE_CURRENT_SOURCE_DIR}/../lwip)
+include(${LWIP_DIR}/contrib/ports/CMakeCommon.cmake)
+
+set (LWIP_DEFINITIONS -DLWIP_DEBUG)
+set (LWIP_INCLUDE_DIRS
+    "${LWIP_DIR}/.."
+    "${LWIP_DIR}/src/include"
+    "${LWIP_CONTRIB_DIR}/"
+    "${LWIP_CONTRIB_DIR}/ports/unix/port/include"
+    "${CMAKE_CURRENT_SOURCE_DIR}/"
+)
+
+include(${LWIP_CONTRIB_DIR}/ports/unix/Filelists.cmake)
+include(${LWIP_DIR}/src/Filelists.cmake)
+
+add_library(lwip ${lwipnoapps_SRCS} ${lwipcontribportunix_SRCS} ${lwipcontribportunixnetifs_SRCS})
+target_compile_options(lwip PRIVATE ${LWIP_COMPILER_FLAGS} -m32)
+target_compile_definitions(lwip PRIVATE ${LWIP_DEFINITIONS} ${LWIP_MBEDTLS_DEFINITIONS})
+target_include_directories(lwip PRIVATE ${LWIP_INCLUDE_DIRS} ${LWIP_MBEDTLS_INCLUDE_DIRS})
+target_link_libraries(lwip ${LWIP_SANITIZER_LIBS})
+
+find_library(LIBPTHREAD pthread)
+target_link_libraries(lwip ${LIBPTHREAD})

Sming/Arch/Host/Components/lwip/Linux/Makefile

@@ -0,0 +1,4 @@
+
+all:
+	cd $(BUILD_DIR); cmake $(CURDIR)
+	make -C $(BUILD_DIR)

Sming/Arch/Host/Components/lwip/lwip.patch

@@ -1,109 +1,3 @@
-diff --git a/contrib/ports/unix/lib/CMakeLists.txt b/contrib/ports/unix/lib/CMakeLists.txt
-index 93d17bd0..d38cf5ff 100644
---- a/contrib/ports/unix/lib/CMakeLists.txt
-+++ b/contrib/ports/unix/lib/CMakeLists.txt
-@@ -2,7 +2,7 @@ cmake_minimum_required(VERSION 3.8)
-
- project(lwip C)
-
--set (BUILD_SHARED_LIBS ON)
-+set (BUILD_SHARED_LIBS OFF)
-
- if (NOT CMAKE_SYSTEM_NAME STREQUAL "Linux" AND NOT CMAKE_SYSTEM_NAME STREQUAL "GNU")
-     message(FATAL_ERROR "Lwip shared library is only working on Linux or the Hurd")
-@@ -23,7 +23,7 @@ include(${LWIP_CONTRIB_DIR}/ports/unix/Filelists.cmake)
- include(${LWIP_DIR}/src/Filelists.cmake)
-
- add_library(lwip ${lwipnoapps_SRCS} ${lwipcontribportunix_SRCS} ${lwipcontribportunixnetifs_SRCS})
--target_compile_options(lwip PRIVATE ${LWIP_COMPILER_FLAGS})
-+target_compile_options(lwip PRIVATE ${LWIP_COMPILER_FLAGS} -m32)
- target_compile_definitions(lwip PRIVATE ${LWIP_DEFINITIONS} ${LWIP_MBEDTLS_DEFINITIONS})
- target_include_directories(lwip PRIVATE ${LWIP_INCLUDE_DIRS} ${LWIP_MBEDTLS_INCLUDE_DIRS})
- target_link_libraries(lwip ${LWIP_SANITIZER_LIBS})
-diff --git a/contrib/ports/unix/lib/lwipopts.h b/contrib/ports/unix/lib/lwipopts.h
-index 660f7f70..94400b99 100644
---- a/contrib/ports/unix/lib/lwipopts.h
-+++ b/contrib/ports/unix/lib/lwipopts.h
-@@ -319,5 +319,5 @@
-  * LWIP_DNS==1: Turn on DNS module. UDP must be available for DNS
-  * transport.
-  */
--#define LWIP_DNS                        0
-+#define LWIP_DNS                        0
-
-diff --git a/contrib/ports/unix/lib/lwipopts.h b/contrib/ports/unix/lib/lwipopts.h
-index 660f7f70..c0affbdd 100644
---- a/contrib/ports/unix/lib/lwipopts.h
-+++ b/contrib/ports/unix/lib/lwipopts.h
-@@ -62,7 +62,7 @@
-  * NO_SYS==1: Provides VERY minimal functionality. Otherwise,
-  * use lwIP facilities.
-  */
--#define NO_SYS                          0
-+#define NO_SYS                          1
-
- /*
-    ------------------------------------
-@@ -150,27 +150,27 @@
-  * MEMP_NUM_NETBUF: the number of struct netbufs.
-  * (only needed if you use the sequential API, like api_lib.c)
-  */
--#define MEMP_NUM_NETBUF                 2
-+#define MEMP_NUM_NETBUF                 0
-
- /**
-  * MEMP_NUM_NETCONN: the number of struct netconns.
-  * (only needed if you use the sequential API, like api_lib.c)
-  */
--#define MEMP_NUM_NETCONN               32
-+#define MEMP_NUM_NETCONN               0
-
- /**
-  * MEMP_NUM_TCPIP_MSG_API: the number of struct tcpip_msg, which are used
-  * for callback/timeout API communication.
-  * (only needed if you use tcpip.c)
-  */
--#define MEMP_NUM_TCPIP_MSG_API          8
-+#define MEMP_NUM_TCPIP_MSG_API          4
-
- /**
-  * MEMP_NUM_TCPIP_MSG_INPKT: the number of struct tcpip_msg, which are used
-  * for incoming packets.
-  * (only needed if you use tcpip.c)
-  */
--#define MEMP_NUM_TCPIP_MSG_INPKT        8
-+#define MEMP_NUM_TCPIP_MSG_INPKT        4
-
- /**
-  * PBUF_POOL_SIZE: the number of buffers in the pbuf pool.
-@@ -319,7 +319,7 @@
-  * LWIP_DNS==1: Turn on DNS module. UDP must be available for DNS
-  * transport.
-  */
--#define LWIP_DNS                        0
-+#define LWIP_DNS                        1
-
- /*
-    ---------------------------------
-@@ -382,7 +382,7 @@
- /**
-  * LWIP_NETCONN==1: Enable Netconn API (require to use api_lib.c)
-  */
--#define LWIP_NETCONN                    1
-+#define LWIP_NETCONN                    0
-
- /*
-    ------------------------------------
-@@ -392,7 +392,7 @@
- /**
-  * LWIP_SOCKET==1: Enable Socket API (require to use sockets.c)
-  */
--#define LWIP_SOCKET                     1
-+#define LWIP_SOCKET                     0
-
- /**
-  * SO_REUSE==1: Enable SO_REUSEADDR
-
 diff --git a/contrib/ports/unix/port/sys_arch.c b/contrib/ports/unix/port/sys_arch.c
 index a56d7de1..dd3f16e1 100644
 --- a/contrib/ports/unix/port/sys_arch.c