* errors.h (warning, error, fatal, internal_error): Mark as cold.
	* predict.c (maybe_hot_bb): Cold functions are never hot; hot functions
	are hot.
	(probably_cold_bb_p): Cold functions are cold.
	(probably_never_executed_bb_p): Cold functions are cold.
	(tree_bb_level_predictions): Predict calls to cold functions as not
	taken.
	(compute_function_frequency): Check hot/cold attributes.
	* function.h (function_frequency): Update comments.
	* predict.def (PRED_COLD_FUNCTION): Predict cold function.
	* c-common.c (handle_hot_attribute, handle_cold_attribute): New.
	(c_common_att): Add cold and hot.

	* doc/extend.texi (hot,cold attributes): Document.
	
	* ansidecl.h (ATTRIBUTE_COLD, ATTRIBUTE_HOT): New.

From-SVN: r122632