Adjust major collection heuristics for OOM scenarios.

Adjust major collection heuristics for OOM scenarios.

	* sgen-gc.c (need_major_collection): Add a space_needed
	parameter that is checked against the available space
	quota.

	* sgen-gc.c (alloc_degraded): Adjust call to
	need_major_collection. Pass zero as space_needed since
	it's won't help to do a major gc if we're already doing
	degrated alloc and old gen is full.

	* sgen-gc.c (alloc_large_inner): Pass size to
	need_major_collection as shrinking major might be needed
	to meet the space quota for.