avr.c (avr_OS_task_function_p): Add new function.

avr.c (avr_OS_task_function_p): Add new function.

	* config/avr/avr.c (avr_OS_task_function_p): Add new function.
	(avr_regs_to_save): Handle functions with 'OS_task' attribute.
	(avr_simple_epilogue, expand_prologue, avr_asm_function_end_prologue,
	expand_epilogue, output_movhi): Don't handle 'main' function.
	(avr_attribute_table): Add 'OS_task' function attribute.
	* config/avr/avr.h (machine_function): Remove 'is_main' field, add
	'is_OS_task' field.
	* config/avr/avr.md (return_from_main_epilogue): Remove insn.
	(return_from_epilogue, return_from_interrupt_epilogue): Don't handle
	'main' function.
	* config/avr/avr.opt (minit-stack): Remove.

From-SVN: r129662