Move TYPE_SELF_TYPE into new field type_specific.

Move TYPE_SELF_TYPE into new field type_specific.

This patch moves TYPE_SELF_TYPE into new field type_specific.self_type
for MEMBERPTR,METHODPTR types, and into type_specific.func_stuff
for METHODs, and then updates everything to use that.
TYPE_CODE_METHOD could share some things with TYPE_CODE_FUNC
(e.g. TYPE_NO_RETURN) and it seemed simplest to keep them together.

Moving TYPE_SELF_TYPE into type_specific.func_stuff for TYPE_CODE_METHOD
is also nice because when we allocate space for function types we assume
they're TYPE_CODE_FUNCs. If TYPE_CODE_METHODs don't need or use that
space then that space would be wasted, and cleaning that up would involve
more invasive changes.

In order to catch errant uses I've added accessor functions
that do some checking.

One can no longer assign to TYPE_SELF_TYPE like this:

  TYPE_SELF_TYPE (foo) = bar;

One instead has to do:

  set_type_self_type (foo, bar);

But I've left reading of the type to the macro:

  bar = TYPE_SELF_TYPE (foo);

In order to discourage bypassing the TYPE_SELF_TYPE macro
I've named the underlying function that implements it
internal_type_self_type.

While testing this I found the stabs reader leaving methods
as TYPE_CODE_FUNCs, hitting my newly added asserts.
Since the dwarf reader smashes functions to methods (via
smash_to_method) I've done a similar thing for stabs.

gdb/ChangeLog:

	* cp-valprint.c (cp_find_class_member): Rename parameter domain_p
	to self_p.
	(cp_print_class_member): Rename local domain to self_type.
	* dwarf2read.c (quirk_gcc_member_function_pointer): Rename local
	domain_type to self_type.
	(set_die_type) <need_gnat_info>: Handle
	TYPE_CODE_METHODPTR, TYPE_CODE_MEMBERPTR, TYPE_CODE_METHOD.
	* gdb-gdb.py (StructMainTypePrettyPrinter): Handle
	TYPE_SPECIFIC_SELF_TYPE.
	* gdbtypes.c (internal_type_self_type): New function.
	(set_type_self_type): New function.
	(smash_to_memberptr_type): Rename parameter domain to self_type.
	Update setting of TYPE_SELF_TYPE.
	(smash_to_methodptr_type): Update setting of TYPE_SELF_TYPE.
	(smash_to_method_type): Rename parameter domain to self_type.
	Update setting of TYPE_SELF_TYPE.
	(check_stub_method): Call smash_to_method_type.
	(recursive_dump_type): Handle TYPE_SPECIFIC_SELF_TYPE.
	(copy_type_recursive): Ditto.
	* gdbtypes.h (enum type_specific_kind): New value
	TYPE_SPECIFIC_SELF_TYPE.
	(struct main_type) <type_specific>: New member self_type.
	(struct cplus_struct_type) <fn_field.type>: Update comment.
	(TYPE_SELF_TYPE): Rewrite.
	(internal_type_self_type, set_type_self_type): Declare.
	* gnu-v3-abi.c (gnuv3_print_method_ptr): Rename local domain to
	self_type.
	(gnuv3_method_ptr_to_value): Rename local domain_type to self_type.
	* m2-typeprint.c (m2_range): Replace TYPE_SELF_TYPE with
	TYPE_TARGET_TYPE.
	* stabsread.c (read_member_functions): Mark methods with
	TYPE_CODE_METHOD, not TYPE_CODE_FUNC.  Update setting of
	TYPE_SELF_TYPE.