stmhal: Support frozen packages using .mpy files.

See issue #1814.

stmhal/Makefile

@@ -284,24 +284,22 @@ endif
 ifneq ($(FROZEN_MPY_DIR),)
 # To use frozen bytecode, put your .py files in a subdirectory (eg frozen/) and
 # then invoke make with FROZEN_MPY_DIR=frozen (be sure to build from scratch).
-FROZEN_MPY_PY_FILES := $(wildcard $(FROZEN_MPY_DIR)/*.py)
+FROZEN_MPY_PY_FILES := $(shell find $(FROZEN_MPY_DIR)/ -type f -name '*.py')
 FROZEN_MPY_MPY_FILES := $(addprefix $(BUILD)/,$(FROZEN_MPY_PY_FILES:.py=.mpy))
 CFLAGS += -DMICROPY_QSTR_EXTRA_POOL=mp_qstr_frozen_const_pool
 CFLAGS += -DMICROPY_MODULE_FROZEN_MPY
-OBJ += $(BUILD)/$(FROZEN_MPY_DIR)/frozen_mpy.o
+OBJ += $(BUILD)/$(BUILD)/frozen_mpy.o
 MPY_CROSS = ../mpy-cross/mpy-cross
 MPY_TOOL = ../tools/mpy-tool.py
 
 $(BUILD)/$(FROZEN_MPY_DIR)/%.mpy: $(FROZEN_MPY_DIR)/%.py
 	@$(ECHO) "MPY $<"
-	$(Q)$(MPY_CROSS) -o $@ $^
+	$(Q)$(MKDIR) -p $(dir $@)
+	$(Q)$(MPY_CROSS) -o $@ -s $(^:$(FROZEN_MPY_DIR)/%=%) $^
 
-$(BUILD)/$(FROZEN_MPY_DIR)/frozen_mpy.c: $(FROZEN_MPY_MPY_FILES) $(BUILD)/genhdr/qstrdefs.generated.h
+$(BUILD)/frozen_mpy.c: $(FROZEN_MPY_MPY_FILES) $(BUILD)/genhdr/qstrdefs.generated.h
 	@$(ECHO) "Creating $@"
 	$(Q)$(PYTHON) $(MPY_TOOL) -f -q $(BUILD)/genhdr/qstrdefs.preprocessed.h $(FROZEN_MPY_MPY_FILES) > $@
-
-$(BUILD)/$(FROZEN_MPY_DIR)/frozen_mpy.o: $(BUILD)/$(FROZEN_MPY_DIR)/frozen_mpy.c
-	$(call compile_c)
 endif
 
 .PHONY: deploy