Improve performance of byte-swapped I/O.

2013-01-23  Janne Blomqvist  <jb@gcc.gnu.org>

	* io/file_pos.c (unformatted_backspace): Use __builtin_bswapXX
	instead of reverse_memcpy.
	* io/io.h (reverse_memcpy): Remove prototype.
	* io/transfer.c (reverse_memcpy): Make static, move towards
	beginning of file.
	(bswap_array): New function.
	(unformatted_read): Use bswap_array to byte swap the data
	in-place.
	(unformatted_write): Use a larger temp buffer and bswap_array.
	(us_read): Use __builtin_bswapXX instead of reverse_memcpy.
	(write_us_marker): Likewise.

From-SVN: r195413