extmod.mk: Allow prebuilt MBEDTLS.

Some systems might have MBEDTLS ported, this allows using that
instead of submodule.

Signed-off-by: Yanfeng Liu <[email protected]>

Author: yf13

extmod/extmod.mk

@@ -242,6 +242,11 @@ SRC_THIRDPARTY_C += $(addprefix $(AXTLS_DIR)/,\
 	crypto/sha1.c \
 	)
 else ifeq ($(MICROPY_SSL_MBEDTLS),1)
+ifeq (${MBEDTLS_PREBUILT},1)     # Use prebuilt mbedtls
+MBEDTLS_CONFIG_FILE ?= \"mbedtls/mbedtls_config_port.h\"
+CFLAGS_EXTMOD += -DMICROPY_SSL_MBEDTLS=1
+CFLAGS_EXTMOD += -DMBEDTLS_CONFIG_FILE=$(MBEDTLS_CONFIG_FILE)
+else                             # Use mbedtls submodule
 MBEDTLS_DIR = lib/mbedtls
 MBEDTLS_CONFIG_FILE ?= \"mbedtls/mbedtls_config_port.h\"
 GIT_SUBMODULES += $(MBEDTLS_DIR)
@@ -329,6 +334,7 @@ SRC_THIRDPARTY_C += $(addprefix $(MBEDTLS_DIR)/library/,\
 	)
 endif
 endif
+endif
 
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 # lwip