esp8266: Enable btree module.

esp8266/Makefile

@@ -5,6 +5,7 @@ QSTR_DEFS = qstrdefsport.h #$(BUILD)/pins_qstr.h
 
 MICROPY_PY_USSL = 1
 MICROPY_SSL_AXTLS = 1
+MICROPY_PY_BTREE = 1
 
 # include py core make definitions
 include ../py/py.mk
@@ -88,6 +89,7 @@ SRC_C = \
 	$(BUILD)/frozen.c \
 	fatfs_port.c \
 	axtls_helpers.c \
+	$(SRC_MOD)
 
 STM_SRC_C = $(addprefix stmhal/,\
 	pybstdio.c \

esp8266/esp8266.ld

@@ -121,6 +121,7 @@ SECTIONS
 
         *lib/fatfs/*.o*(.literal*, .text*)
         */libaxtls.a:(.literal*, .text*)
+        *lib/berkeley-db-1.xx/*.o(.literal*, .text*)
         *lib/libm/*.o*(.literal*, .text*)
         *lib/mp-readline/*.o(.literal*, .text*)
         *lib/netutils/*.o*(.literal*, .text*)