rp2/mpconfigport.h: Allow boards to override internal errno config.

ports/rp2/mpconfigport.h

@@ -66,9 +66,11 @@
 #define MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF  (1)
 #define MICROPY_LONGINT_IMPL                    (MICROPY_LONGINT_IMPL_MPZ)
 #define MICROPY_FLOAT_IMPL                      (MICROPY_FLOAT_IMPL_FLOAT)
-#define MICROPY_USE_INTERNAL_ERRNO              (1)
 #define MICROPY_SCHEDULER_DEPTH                 (8)
 #define MICROPY_SCHEDULER_STATIC_NODES          (1)
+#ifndef MICROPY_USE_INTERNAL_ERRNO
+#define MICROPY_USE_INTERNAL_ERRNO              (1)
+#endif
 
 // Fine control over Python builtins, classes, modules, etc
 #define MICROPY_PY_BUILTINS_HELP_TEXT           rp2_help_text