c++/modules: Support ADL on non-discarded GM entities [PR121705]HEADtrunkmaster

[basic.lookup.argdep] p4 says that ADL also finds declarations of
functions or function templates from a point of lookup within the
module, only ignoring discarded (or internal) GM entities.

To implement this we need to create bindings for these entities so that
we can guarantee that name lookup will discover they exist.  This raises
some complications, though, as we ideally would like to avoid having
bindings that contain no declarations, or emitting GM namespaces that
only contain discarded or internal functions.

This patch does this by additionally creating a new binding whenever we
call make_dependency on a non-EK_FOR_BINDING decl.  We don't do this for
using-decls, as at the point of use of a GM entity we no longer know
whether we called through a using-decl or the declaration directly;
however, this behaviour is explicitly supported by [module.global.frag]
p3.6.

Creating these bindings caused g++.dg/modules/default-arg-4_* to fail.
It turns out that this makes the behaviour look identical to
g++.dg/modules/default-arg-5, which is incorrectly dg-error-ing default
value redeclarations (we only currently error because of PR c++/99000).
This patch removes the otherwise identical test and turns the dg-errors
into xfailed dg-bogus.

As a drive-by fix this also fixes an ICE when debug printing friend
function instantiations.

	PR c++/121705
	PR c++/117658

gcc/cp/ChangeLog:

	* module.cc (depset::hash::make_dependency): Make bindings for
	GM functions.
	(depset::hash::add_binding_entity): Adjust comment.
	(depset::hash::add_deduction_guides): Add log.
	* ptree.cc (cxx_print_xnode): Handle friend functions where
	TI_TEMPLATE is an OVERLOAD or IDENTIFIER.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/default-arg-4_a.C: XFAIL bogus errors.
	* g++.dg/modules/default-arg-4_b.C: Likewise.
	* g++.dg/modules/default-arg-5_a.C: Remove duplicate test.
	* g++.dg/modules/default-arg-5_b.C: Likewise.
	* g++.dg/modules/adl-9_a.C: New test.
	* g++.dg/modules/adl-9_b.C: New test.
	* g++.dg/modules/gmf-5.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>

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