Validate and set default parameters for stack-clash.

Validate and set default parameters for stack-clash.

This patch defines the default parameters and validation for the aarch64
stack clash probing interval and guard sizes.  It cleans up the previous
implementation and insures that at no point the invalidate arguments are
present in the pipeline for AArch64.  Currently they are only corrected once
cc1 initalizes the back-end.

The default for AArch64 is 64 KB for both of these and we only support 4 KB and 64 KB
probes.  We also enforce that any value you set here for the parameters must be
in sync.

If an invalid value is specified an error will be generated and compilation aborted.

gcc/

	* common/config/aarch64/aarch64-common.c (TARGET_OPTION_DEFAULT_PARAM,
	aarch64_option_default_param):	New.
	(params.h): Include.
	(TARGET_OPTION_VALIDATE_PARAM, aarch64_option_validate_param): New.
	* config/aarch64/aarch64.c (aarch64_override_options_internal): Simplify
	stack-clash protection validation code.

From-SVN: r264757