Introduce partial_symtab::expand_psymtab method

Introduce partial_symtab::expand_psymtab method

The symbol readers generally used two functions to expand a partial
symtab: an outer function (now the "read_symtab" method), and an inner
function, typically named something like "psymtab_to_symtab".

This patch changes this second step to be a method on partial_symtab,
and updates all the callers.  For legacy_psymtab, a new function
pointer member is introduced.

This patch enables a subsequent cleanup.

gdb/ChangeLog
2020-01-26  Tom Tromey  <tom@tromey.com>

	* xcoffread.c (xcoff_psymtab_to_symtab_1): Change argument order.
	Call expand_psymtab.
	(xcoff_read_symtab): Call expand_psymtab.
	(xcoff_start_psymtab, xcoff_end_psymtab): Set
	legacy_expand_psymtab.
	* psympriv.h (struct partial_symtab) <expand_psymtab>: New
	method.
	(struct legacy_psymtab) <expand_psymtab>: Implement.
	<legacy_expand_psymtab>: New member.
	* mdebugread.c (mdebug_read_symtab): Call expand_psymtab.
	(parse_partial_symbols): Set legacy_expand_psymtab.
	(psymtab_to_symtab_1): Change argument order.  Call
	expand_psymtab.
	(new_psymtab): Set legacy_expand_psymtab.
	* dwarf2read.h (struct dwarf2_psymtab) <expand_psymtab>: Declare.
	* dwarf2read.c (dwarf2_psymtab::read_symtab): Call
	expand_psymtab.
	(dwarf2_psymtab::expand_psymtab): Rename from
	psymtab_to_symtab_1.  Call expand_psymtab.
	* dbxread.c (start_psymtab): Set legacy_expand_psymtab.
	(dbx_end_psymtab): Likewise.
	(dbx_psymtab_to_symtab_1): Change argument order. Call
	expand_psymtab.
	(dbx_read_symtab): Call expand_psymtab.
	* ctfread.c (struct ctf_psymtab) <expand_psymtab>: Declare.
	(ctf_psymtab::expand_psymtab): Rename from psymtab_to_symtab.
	(ctf_psymtab::read_symtab): Call expand_psymtab.

Change-Id: Ic39a2d7aa7b424088d910b59dbd21271fa1c3430