use CFLAG to properly set define

ports/stm32f4/mpconfigport.mk

@@ -69,7 +69,7 @@ ifndef CIRCUITPY_DISPLAYIO
 CIRCUITPY_DISPLAYIO = 1
 endif
 
-MICROPY_CPYTHON_COMPAT = 1
+CFLAGS += -DMICROPY_CPYTHON_COMPAT=1
 
 #ifeq ($(MCU_SUB_VARIANT), stm32f412zx)
 #endif

py/circuitpy_mpconfig.h

@@ -182,7 +182,10 @@ typedef long mp_off_t;
 
 // Remove some lesser-used functionality to make small builds fit.
 #define MICROPY_BUILTIN_METHOD_CHECK_SELF_ARG (CIRCUITPY_FULL_BUILD)
-#define MICROPY_CPYTHON_COMPAT                (CIRCUITPY_FULL_BUILD)
+//TODO: replace this with a rework of the FULL_BUILD system
+#if !defined(MICROPY_CPYTHON_COMPAT)
+	#define MICROPY_CPYTHON_COMPAT                (CIRCUITPY_FULL_BUILD)
+#endif
 #define MICROPY_MODULE_WEAK_LINKS             (CIRCUITPY_FULL_BUILD)
 #define MICROPY_PY_ALL_SPECIAL_METHODS        (CIRCUITPY_FULL_BUILD)
 #define MICROPY_PY_BUILTINS_COMPLEX           (CIRCUITPY_FULL_BUILD)