[16/77] Add scalar_int_mode_pod

[16/77] Add scalar_int_mode_pod

This patch adds a POD class for scalar integers, as an instance
of a new pod_mode template.  Later patches will use pod_mode in
situations that really do need to be POD; this patch is simply
using PODs to remove load-time initialisation.

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

gcc/
	* coretypes.h (pod_mode): New type.
	(scalar_int_mode_pod): New typedef.
	* machmode.h (pod_mode): New class.
	(int_n_data_t::m): Change type to scalar_int_mode_pod.
	* genmodes.c (emit_mode_int_n): Update accordingly.
	* lower-subreg.h (target_lower_subreg): Change type to
	scalar_int_mode_pod.
	* gdbhooks.py (build_pretty_printer): Handle pod_mode and
	scalar_int_mode_pod.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r251468