gimple-fold.c (gimple_fold_builtin_memory_op): Use gimple_build and get rid of force_gimple_operand_gsi.

2015-10-16  Richard Biener  <rguenther@suse.de>

	* gimple-fold.c (gimple_fold_builtin_memory_op): Use gimple_build
	and get rid of force_gimple_operand_gsi.
	(gimple_fold_builtin_memory_chk): Likewise.
	(gimple_fold_builtin_stxcpy_chk): Likewise.
	(rewrite_to_defined_overflow): Likewise.
	(gimple_convert_to_ptrofftype): New function.
	* gimple-fold.h (gimple_convert_to_ptrofftype): New overload,
	declare.

From-SVN: r228863