Convert the DWARF reader to new-style buildysm

Convert the DWARF reader to new-style buildysm

This converts the DWARF reader to use the new-style buildsym API.  A
new buildsym_compunit is created for each CU and is used to construct
the symbol table.  In some cases the CU must be passed to functions
which previously did not accept it.  FWIW I tend to think that most
methods in the DWARF reader ought to be methods on the dwarf2_cu
object.

gdb/ChangeLog
2018-07-20  Tom Tromey  <tom@tromey.com>

	* dwarf2read.c: Include buildsym.h.
	(struct dwarf2_cu) <builder>: New method.
	(fixup_go_packaging): Update.
	(process_full_comp_unit, process_full_type_unit): Update.  Don't
	use scoped_free_pendings.
	(using_directives): Add "cu" parameter, remove "language".
	(read_import_statement, setup_type_unit_groups, )
	(read_func_scope, read_lexical_block_scope)
	(dwarf2_record_block_ranges, read_namespace): Update.
	(lnp_state_machine::lnp_state_machine): Add cu parameter.
	(lnp_state_machine::handle_end_sequence): Update.
	(class lnp_state_machine) <m_cu>: New member.
	<m_record_line_callback>: Remove.
	<m_currently_recording_lines>: New member.
	(lnp_state_machine::handle_set_file): Update.
	(noop_record_line): Remove.
	(dwarf_record_line_p): Add cu parameter.
	(dwarf_record_line_1, dwarf_finish_line): Likewise.
	(lnp_state_machine::record_line)
	(lnp_state_machine::lnp_state_machine)
	(lnp_state_machine::check_line_address, dwarf_decode_lines_1)
	(dwarf_decode_lines): Update.
	(dwarf2_start_subfile): Add cu parameter.
	(dwarf2_start_symtab, new_symbol): Update.
	(macro_start_file, dwarf_decode_macro_bytes): Add cu parameter.
	Remove dwarf2_per_objfile parameter.
	(dwarf_decode_macros): Update.