Consider addressable memory unit size in various value functions

Consider addressable memory unit size in various value functions

This patch updates various value handling functions to make them
consider the addressable memory unit size of the current architecture.
This allows to correctly extract and print values on architectures whose
addressable memory unit is not 8 bits.

The patch doesn't cover all the code that would ideally need to be
adjusted, only the code paths that we happen to use, plus a few obvious
ones.  Specifically, those areas are not covered by this patch:

 - Management of unavailable bits
 - Bitfields
 - C++ stuff

Regression-tested on x86-64 Ubuntu 14.04.  I saw no related test result
change.

gdb/ChangeLog:

	* c-valprint.c (c_val_print_array): Consider addressable memory
	unit size.
	(c_val_print_ptr): Likewise.
	(c_val_print_int): Likewise.
	* findvar.c (read_frame_register_value): Likewise.
	* valarith.c (find_size_for_pointer_math): Likewise.
	(value_ptrdiff): Likewise.
	(value_subscripted_rvalue): Likewise.
	* valops.c (read_value_memory): Likewise (and rename variables).
	(value_assign): Likewise.
	(value_repeat): Likewise.
	(value_array): Likewise.
	(value_slice): Likewise.
	* valprint.c (generic_val_print_ptr): Likewise.
	(generic_val_print_enum): Likewise.
	(generic_val_print_bool): Likewise.
	(generic_val_print_int): Likewise.
	(generic_val_print_char): Likewise.
	(generic_val_print_float): Likewise.
	(generic_val_print_decfloat): Likewise.
	(generic_val_print_complex): Likewise.
	(val_print_scalar_formatted): Likewise.
	(val_print_array_elements): Likewise.
	* value.c (set_value_parent): Likewise.
	(value_contents_copy_raw): Likewise.
	(set_internalvar_component): Likewise.
	(value_primitive_field): Likewise.
	(value_fetch_lazy): Likewise.
	* value.h (read_value_memory): Update comment.