Use functions and constants to manipulate Lisp_Save_Value objects.

Use functions and constants to manipulate Lisp_Save_Value objects.

This replaces code that used macros and strings and token-pasting.
The change makes the C source a bit easier to follow,
and shrinks the Emacs executable a bit.
* alloc.c: Verify some properties of Lisp_Save_Value's representation.
(make_save_value): Change 1st arg from string to enum.  All callers
changed.
(INTX): Remove.
(mark_object): Use if, not #if, for GC_MARK_STACK.
* lisp.h (SAVE_VALUEP, XSAVE_VALUE, XSAVE_POINTER, XSAVE_INTEGER)
(XSAVE_OBJECT): Now functions, not macros.
(STRING_BYTES_BOUND): Now just a macro, not a constant too;
the constant was never used.
(SAVE_SLOT_BITS, SAVE_VALUE_SLOTS, SAVE_TYPE_BITS, SAVE_TYPE_INT_INT)
(SAVE_TYPE_INT_INT_INT, SAVE_TYPE_OBJ_OBJ, SAVE_TYPE_OBJ_OBJ_OBJ)
(SAVE_TYPE_OBJ_OBJ_OBJ_OBJ, SAVE_TYPE_PTR_INT, SAVE_TYPE_PTR_OBJ)
(SAVE_TYPE_PTR_PTR, SAVE_TYPE_PTR_PTR_OBJ, SAVE_TYPE_MEMORY):
New constants.
(struct Lisp_Save_Value): Replace members area, type0, type1, type2,
type3 with a single member save_type.  All uses changed.
(save_type, set_save_pointer, set_save_integer): New functions.
* print.c (PRINTX): Remove.