dwarf2: Emit DW_TAG_unspecified_parameters even in late DWARF [PR97599]

dwarf2: Emit DW_TAG_unspecified_parameters even in late DWARF [PR97599]

Aldy's PR71855 fix avoided emitting multiple redundant
DW_TAG_unspecified_parameters sub-DIEs of a single DIE by restricting
it to early dwarf only.  That unfortunately means if we need to emit
another DIE for the function (whether it is for LTO, or e.g. because of
IPA cloning), we don't emit DW_TAG_unspecified_parameters, it remains
solely in the DW_AT_abstract_origin's referenced DIE.
But DWARF consumers don't really use DW_TAG_unspecified_parameters
from there, like we duplicate DW_TAG_formal_parameter sub-DIEs even in the
clones because either they have some more specific location, or e.g.
a function clone could have fewer or different argument types etc.,
they need to assume that originally stdarg function isn't later stdarg etc.
Unfortunately, while for DW_TAG_formal_parameter sub-DIEs, we can use the
hash tabs to look the PARM_DECLs if we already have the DIEs, for
DW_TAG_unspecified_parameters we don't have an easy way to look it up.

The following patch handles it by trying to figure out if we are creating a
fresh new DIE (in that case we add DW_TAG_unspecified_parameters if it is
stdarg), or if gen_subprogram_die is called again on an pre-existing DIE
to fill in some further details (then it will not touch it).

Except for lto, subr_die != old_die would be good enough, but unfortunately
for LTO the new DIE that will refer to early dwarf created DIE is created
on the fly during lookup_decl_die.  So the patch tracks if the DIE has
no children before any children are added to it.

2020-11-14  Jakub Jelinek  <jakub@redhat.com>

	PR debug/97599
	* dwarf2out.c (gen_subprogram_die): Call
	gen_unspecified_parameters_die even if not early dwarf, but only
	if subr_die is a newly created DIE.