gimple-ssa-store-merging.c (struct merged_store_group): Move up bit_insertion field and declare can_be_merged_into method.

	* gimple-ssa-store-merging.c (struct merged_store_group): Move up
	bit_insertion field and declare can_be_merged_into method.
	(merged_store_group::can_be_merged_into): New method.
	(imm_store_chain_info::coalesce_immediate): Call it to decide whether
	consecutive non-overlapping stores can be merged.  Turn MEM_REF stores
	into BIT_INSERT_EXPR stores if the group contains a non-MEM_REF store.

From-SVN: r261173