Hello. After this revision I see:
$ ../configure --target=avr-elf --enable-languages=c,c++ --disable-bootstrap $ make ../../gcc/config/avr/avr.c: In function ‘void avr_option_override()’: ../../gcc/config/avr/avr.c:778:29: error: lvalue required as left operand of assignment TARGET_GASISR_PROLOGUES = 0; ^