Allow setting of stack-clash via configure options.

Allow setting of stack-clash via configure options.

This patch defines a configure option to allow the setting of the default
guard size via configure flags when building the target.

The new flag is:

 * --with-stack-clash-protection-guard-size=<num>

The patch defines a new macro DEFAULT_STK_CLASH_GUARD_SIZE which targets need
to use explicitly is they want to support this configure flag and values that
users may have set.

gcc/

	PR target/86486
	* configure.ac: Add stack-clash-protection-guard-size.
	* doc/install.texi: Document it.
	* config.in (DEFAULT_STK_CLASH_GUARD_SIZE): New.
	* params.def: Update comment for guard-size.
	(PARAM_STACK_CLASH_PROTECTION_GUARD_SIZE,
	PARAM_STACK_CLASH_PROTECTION_PROBE_INTERVAL): Update description.
	* configure: Regenerate.

From-SVN: r264752