Attach partial symtab storage to psymbol_functions

Attach partial symtab storage to psymbol_functions

Currently, the storage for partial symtabs is attached to the objfile.
Ultimately, though, this direct assocation will be removed, and the
storage will be owned by the psymbol_functions object.

This patch is a step toward this goal.  The storage is already managed
as a shared_ptr, to enable cross-objfile sharing, so this adds a
reference from the psymbol_functions, and changes some code in
psymtab.c to use this reference instead.

gdb/ChangeLog
2021-03-20  Tom Tromey  <tom@tromey.com>

	* dwarf2/read.c (dwarf2_build_psymtabs): Call
	set_partial_symtabs.
	* symfile.c (syms_from_objfile_1, reread_symbols): Update.
	* psymtab.h (make_psymbol_functions): Add partial_symtabs
	parameter.
	* psymtab.c (find_pc_sect_psymtab): Add partial_symtabs
	parameter.
	(psymbol_functions::find_pc_sect_compunit_symtab)
	(psymbol_functions::print_stats, psymbol_functions::dump)
	(psymbol_functions::has_symbols): Update.
	(make_psymbol_functions, dump_psymtab_addrmap): Add
	partial_symtabs parameter.
	(maintenance_print_psymbols): Update.
	(psymbol_functions::expand_symtabs_matching): Update.
	* psympriv.h (struct psymbol_functions): Add constructor.
	<m_partial_symtabs>: New member.
	<set_partial_symtabs>: New method.