Support << and >> for offset_int and widest_int

Support << and >> for offset_int and widest_int

Following on from the comparison patch, I think it makes sense to
support << and >> for offset_int (int128_t) and widest_int (intNNN_t),
with >> being arithmetic shift.  It doesn't make sense to use
logical right shift on a potentially negative offset_int, since
the precision of 128 bits has no meaning on the target.

Tested on x86_64-linux-gnu and aarch64-linux-gnu.

gcc/
	* wide-int.h: Update offset_int and widest_int documentation.
	(WI_SIGNED_SHIFT_RESULT): New macro.
	(wi::binary_shift): Define signed_shift_result_type for
	shifts on offset_int- and widest_int-like types.
	(generic_wide_int): Support <<= and >>= if << and >> are supported.
	* tree.h (int_bit_position): Use shift operators instead of wi::
	 shifts.
	* alias.c (adjust_offset_for_component_ref): Likewise.
	* expr.c (get_inner_reference): Likewise.
	* fold-const.c (fold_comparison): Likewise.
	* gimple-fold.c (fold_nonarray_ctor_reference): Likewise.
	* gimple-ssa-strength-reduction.c (restructure_reference): Likewise.
	* tree-dfa.c (get_ref_base_and_extent): Likewise.
	* tree-ssa-alias.c (indirect_ref_may_alias_decl_p): Likewise.
	(stmt_kills_ref_p): Likewise.
	* tree-ssa-ccp.c (bit_value_binop_1): Likewise.
	* tree-ssa-math-opts.c (find_bswap_or_nop_load): Likewise.
	* tree-ssa-sccvn.c (copy_reference_ops_from_ref): Likewise.
	(ao_ref_init_from_vn_reference): Likewise.

gcc/cp/
	* init.c (build_new_1): Use shift operators instead of wi:: shifts.

From-SVN: r235720