[12/77] Use opt_scalar_float_mode when iterating over float modes

[12/77] Use opt_scalar_float_mode when iterating over float modes

This means that we know when accessing the modes that the size is
a compile-time constant, even for SVE.  It also enables stricter
type safety in later patches.

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

gcc/
	* machmode.h (mode_iterator::start): Provide overload for opt_modes.
	(mode_iterator::iterate_p): Likewise.
	(mode_iterator::get_wider): Likewise.
	* expr.c (init_expr_target): Use opt_scalar_float_mode.

gcc/ada/
	* gcc-interface/misc.c (fp_prec_to_size): Use opt_scalar_float_mode.
	(fp_size_to_prec): Likewise.

gcc/c-family/
	* c-cppbuiltin.c (c_cpp_builtins): Use opt_scalar_float_mode.

gcc/fortran/
	* trans-types.c (gfc_init_kinds): Use opt_scalar_float_mode
	and FOR_EACH_MODE_IN_CLASS.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r251464