re PR target/46430 (avr-elf --enable-werror-always build fails)

re PR target/46430 (avr-elf --enable-werror-always build fails)

	PR target/46430
	* config/avr/avr-protos.h (avr_return_addr_rtx): Update prototype.
	* config/avr/driver-avr.c (avr_device_to_arch): Always return value.
	(avr_device_to_data_start, avr_device_to_startfiles): Likewise.
	(avr_device_to_devicelib): Likewise.
	* config/avr/avr.md (zero_extendqihi2): Put variable declarations
	into block.
	(zero_extendqisi2, zero_extendhisi2, zero_extendqidi2): Likewise.
	(zero_extendhidi2, zero_extendsidi2): Likewise.
	* config/avr/avr.c (avr_num_arg_regs): Constify type.
	(avr_return_addr_rtx): De-constify tem.
	(avr_rotate_bytes): Move declarations to start of block.
	Don't use variable length array.
	Put nested if/else into block.

From-SVN: r166647