This patch changes it so that default parameters are validated during
initialization. This change is needed to ensure parameters set via by the
target specific common initialization routines still keep the parameters within
the valid range.

gcc/

	* params.c (validate_param): New.
	(add_params): Use it.
	(set_param_value): Refactor param validation into validate_param.
	(diagnostic.h): Include.
	* diagnostic.h (diagnostic_ready_p): New.

From-SVN: r264756