esp8266: Enable uerrno module, weak linked also as errno.

esp8266/mpconfigport.h

@@ -46,6 +46,7 @@
 #define MICROPY_PY_SYS_MAXSIZE      (1)
 #define MICROPY_PY_SYS_EXIT         (1)
 #define MICROPY_PY_SYS_STDFILES     (1)
+#define MICROPY_PY_UERRNO           (1)
 #define MICROPY_PY_UBINASCII        (1)
 #define MICROPY_PY_UCTYPES          (1)
 #define MICROPY_PY_UHASHLIB         (1)
@@ -141,6 +142,7 @@ extern const struct _mp_obj_module_t onewire_module;
     { MP_OBJ_NEW_QSTR(MP_QSTR_time), (mp_obj_t)&utime_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_os), (mp_obj_t)&uos_module }, \
     { MP_OBJ_NEW_QSTR(MP_QSTR_json), (mp_obj_t)&mp_module_ujson }, \
+    { MP_OBJ_NEW_QSTR(MP_QSTR_errno), (mp_obj_t)&mp_module_uerrno }, \
 
 #define MP_STATE_PORT MP_STATE_VM