ports/stm32: Add Zephyr source to qstr extraction for root pointers.

Include ZEPHYR_MP_SRC_C in SRC_QSTR when MICROPY_ZEPHYR_THREADING=1 to
ensure MP_REGISTER_ROOT_POINTER declarations in mpthread_zephyr.c are
extracted and included in genhdr/root_pointers.h.

Without this, the build system doesn't preprocess the Zephyr threading
files and misses the mp_thread_list_head root pointer registration.

Signed-off-by: Andrew Leech <[email protected]>

Author: pi-anl

ports/stm32/Makefile

@@ -680,6 +680,10 @@ $(BUILD)/firmware.elf: $(OBJ)
 
 # List of sources for qstr extraction
 SRC_QSTR += $(SRC_C) $(SRC_CXX) $(SHARED_SRC_C) $(GEN_PINS_SRC)
+# Add MicroPython-Zephyr integration files for root pointer extraction
+ifeq ($(MICROPY_ZEPHYR_THREADING),1)
+SRC_QSTR += $(ZEPHYR_MP_SRC_C)
+endif
 
 # Making OBJ use an order-only dependency on the generated pins.h file
 # has the side effect of making the pins.h file before we actually compile