extmod/modlwip: Clean up inclusion of modlwip in build process.

The following changes are made:

- Guard entire file with MICROPY_PY_LWIP, so it can be included in the
  build while still being disabled (for consistency with other extmod
  modules).

- Add modlwip.c to list of all extmod source in py/py.mk and
  extmod/extmod.cmake so all ports can easily use it.

- Move generic modlwip GIT_SUBMODULES build configuration code from
  ports/rp2/CMakeLists.txt to extmod/extmod.cmake, so it can be reused by
  other ports.

- Remove now unnecessary inclusion of modlwip.c in EXTMOD_SRC_C in esp8266
  port, and in SRC_QSTR in mimxrt port.

Signed-off-by: Damien George <damien@micropython.org>

extmod/extmod.cmake

@@ -16,6 +16,7 @@ set(MICROPY_SOURCE_EXTMOD
     ${MICROPY_EXTMOD_DIR}/modbluetooth.c
     ${MICROPY_EXTMOD_DIR}/modbtree.c
     ${MICROPY_EXTMOD_DIR}/modframebuf.c
+    ${MICROPY_EXTMOD_DIR}/modlwip.c
     ${MICROPY_EXTMOD_DIR}/modnetwork.c
     ${MICROPY_EXTMOD_DIR}/modonewire.c
     ${MICROPY_EXTMOD_DIR}/moduasyncio.c
@@ -246,4 +247,6 @@ if(MICROPY_PY_LWIP)
     list(APPEND MICROPY_INC_CORE
         ${MICROPY_LIB_LWIP_DIR}/include
     )
+
+    string(CONCAT GIT_SUBMODULES "${GIT_SUBMODULES} " lib/lwip)
 endif()

extmod/extmod.mk

@@ -153,7 +153,7 @@ LWIP_DIR = lib/lwip/src
 INC += -I$(TOP)/$(LWIP_DIR)/include
 CFLAGS_MOD += -DMICROPY_PY_LWIP=1
 $(BUILD)/$(LWIP_DIR)/core/ipv4/dhcp.o: CFLAGS_MOD += -Wno-address
-SRC_MOD += extmod/modlwip.c shared/netutils/netutils.c
+SRC_MOD += shared/netutils/netutils.c
 SRC_MOD += $(addprefix $(LWIP_DIR)/,\
 	apps/mdns/mdns.c \
 	core/def.c \

extmod/modlwip.c

@@ -35,6 +35,8 @@
 #include "py/mperrno.h"
 #include "py/mphal.h"
 
+#if MICROPY_PY_LWIP
+
 #include "shared/netutils/netutils.h"
 
 #include "lwip/init.h"
@@ -1741,8 +1743,6 @@ STATIC mp_obj_t lwip_print_pcbs() {
 }
 MP_DEFINE_CONST_FUN_OBJ_0(lwip_print_pcbs_obj, lwip_print_pcbs);
 
-#if MICROPY_PY_LWIP
-
 STATIC const mp_rom_map_elem_t mp_module_lwip_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_lwip) },
     { MP_ROM_QSTR(MP_QSTR_reset), MP_ROM_PTR(&mod_lwip_reset_obj) },

ports/esp8266/Makefile

@@ -109,7 +109,6 @@ SRC_C = \
 	$(SRC_MOD)
 
 EXTMOD_SRC_C = $(addprefix extmod/,\
-	modlwip.c \
 	modonewire.c \
         )
 

ports/mimxrt/Makefile

@@ -150,7 +150,6 @@ SRC_ETH_C += \
 	$(MCU_DIR)/drivers/fsl_enet.c \
 
 SRC_QSTR += \
-	extmod/modlwip.c \
 	extmod/modnetwork.c \
 	extmod/moduwebsocket.c \
 	extmod/modusocket.c \

ports/rp2/CMakeLists.txt

@@ -182,12 +182,6 @@ if (MICROPY_PY_LWIP)
     target_compile_definitions(${MICROPY_TARGET} PRIVATE
         MICROPY_PY_LWIP=1
     )
-
-    list(APPEND MICROPY_SOURCE_EXTMOD
-        ${MICROPY_EXTMOD_DIR}/modlwip.c
-    )
-
-    string(CONCAT GIT_SUBMODULES "${GIT_SUBMODULES} " lib/lwip)
 endif()
 
 if(MICROPY_PY_BLUETOOTH)

py/py.mk

@@ -194,6 +194,7 @@ PY_EXTMOD_O_BASENAME = \
 	extmod/machine_i2c.o \
 	extmod/machine_spi.o \
 	extmod/modbluetooth.o \
+	extmod/modlwip.o \
 	extmod/modussl_axtls.o \
 	extmod/modussl_mbedtls.o \
 	extmod/moduplatform.o\