> In avr.c there is: > > ... > #include "c-family/c-common.h" > ...
That is the problem: avr.c should be language independent. Here you are trying to link code calling C-family functions in a non-C language (lto1 is just another front end for gcc, just like cc1/cc1plus/etc...). You should use extra target files for language specific target code. Plenty examples in config/*/*-c.* ... Ciao! Steven