gdb: Merge auto and unknown language implementations

gdb: Merge auto and unknown language implementations

The auto_language and unknown_language classes are basically the same
except for the language names and store_sym_names_in_linkage_form_p
which the unknown_language overrides to return true, while
auto_language returns the default false.

This commit creates a new parent class from which both of these
languages can inherit.  The two base classes are now greatly reduced.

Some of the static helper functions which previously were called from
both of these languages are now only called from one place, and so
I've inlined them into the new class.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* language.c (default_is_string_type_p): Delete, implementation
	moved into auto_or_unknown_language::is_string_type_p.
	(unk_op_print_tab): Moved into
	auto_or_unknown_language::opcode_print_table.
	(unknown_language_arch_info): Delete, implementation moved into
	auto_or_unknown_language::language_arch_info.
	(class auto_or_unknown_language): New class, member functions
	copied from unknown_language class, with some updates.
	(class unknown_language): Most member functions moved into
	auto_or_unknown_language class.  Inherit from
	auto_or_unknown_language class.
	(class auto_language): Inherit from auto_or_unknown_language.
	Delete most member functions.