re PR target/34299 ([avr] ICE on function attribute syntax for main())

	PR target/34299
	* config/avr/avr.c (avr_handle_fndecl_attribute): Move code for
	generate a warning if the function name does not begin with
	"__vector" and the function has either the 'signal' or 'interrupt'
	attribute, from here to ...
	(avr_declare_function_name): ...here. New function.
	* config/avr/avr.h (ASM_DECLARE_FUNCTION_NAME): Redefine.
	* config/avr/avr-protos.h (avr_declare_function_name): Declare.

From-SVN: r144870