Here is a thread covering your poisoned "SIG_USART1_RECV" messages.
http://arduino.cc/forum/index.php/topic,92364.0.html
That is a deprecated format in avr-libc 1.8.0.
Excuse my ignorance of Gentoo, but do they have this Arduino/AVR code in their repository? If they do, maybe you should contact them about getting that fixed.