[51/77] Use opt_scalar_int_mode when iterating over integer modes

This patch uses opt_scalar_int_mode rather than machine_mode
when iterating over scalar_int_modes, in cases where that helps
with future patches.  (Using machine_mode is still OK in places
that don't really care about the mode being a scalar integer.)

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* cse.c (cse_insn): Use opt_scalar_int_mode for the mode iterator.
	* explow.c (hard_function_value): Likewise.
	* expmed.c (extract_fixed_bit_field_1): Likewise.  Move the
	convert_to_mode call outside the loop.
	* expr.c (alignment_for_piecewise_move): Use opt_scalar_int_mode
	for the mode iterator.  Require the mode specified by max_pieces
	to exist.
	(emit_block_move_via_movmem): Use opt_scalar_int_mode for the
	mode iterator.
	(copy_blkmode_to_reg): Likewise.
	(set_storage_via_setmem): Likewise.
	* optabs.c (prepare_cmp_insn): Likewise.
	* rtlanal.c (init_num_sign_bit_copies_in_rep): Likewise.
	* stor-layout.c (finish_bitfield_representative): Likewise.

gcc/fortran/
	* trans-types.c (gfc_init_kinds): Use opt_scalar_int_mode for
	the mode iterator.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>

From-SVN: r251503