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Error de compilación Clang+AVR: ''= w'' en asm

Question

Recibí el error anterior y no encontré la solución. ¿Alguien sabe cómo resolver?

rafael@ubuntu:~/avr/projeto$ clang -fsyntax-only -Os -I /usr/lib/avr/include -D__AVR_ATmega328P__ -DARDUINO=100 -Wno-ignored-attributes -Wno-attributes serial_tree.c
In file included from serial_tree.c:3:
In file included from /usr/lib/avr/include/util/delay.h:43:
/usr/lib/avr/include/util/delay_basic.h:108:5: error: invalid output
constraint
''=w'' in asm
: "=w" (__count)
^
1 error generated.