avr.md: Fix two 0x80000000 constants to make them negative also on 64-bit hosts.

	* config/avr/avr.md: Fix two 0x80000000 constants to make them
	negative also on 64-bit hosts.

	Default to -fno-reorder-blocks when optimizing for size.
	* config/avr/avr-protos.h (avr_optimization_options): Declare.
	* config/avr/avr.c (avr_optimization_options): New function.
	* config/avr/avr.h (OPTIMIZATION_OPTIONS): New.

	Optimize returning from simple functions.
	* config/avr/avr-protos.h (avr_simple_epilogue): Declare.
	* config/avr/avr.c (avr_simple_epilogue): New function.
	* config/avr/avr.md (return): New insn.

From-SVN: r55378