Change allocate_psymtab to be a constructor

Change allocate_psymtab to be a constructor

This is the next step in getting the symbol readers to allocate
psymtabs themselves: change allocate_psymtab to be an ordinary
constructor, and then use "new" at the previous call sites.  Note that
this doesn't get us all the way -- start_psymtab_common is still
allocating a partial symtab.

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

	* xcoffread.c (xcoff_end_psymtab): Use new.
	* psymtab.c (start_psymtab_common): Use new.
	(partial_symtab::partial_symtab): Rename from allocate_psymtab.
	Update.
	* psympriv.h (struct partial_symtab): Add parameters to
	constructor.  Don't inline.
	(allocate_psymtab): Don't declare.
	* mdebugread.c (new_psymtab): Use new.
	* dwarf2read.c (dwarf2_create_include_psymtab): Use new.
	* dbxread.c (dbx_end_psymtab): Use new.

Change-Id: Iffeae64c925050b90b9916cbc36e15b26ff42226