c++/modules: Fix tsubst of global module friend classes [PR118920]

c++/modules: Fix tsubst of global module friend classes [PR118920]

When doing tsubst_friend_class, we need to first check if any imported
module has already created a (hidden) declaration for the class so that
we don't end up with conflicting declarations.  Currently we do this
using DECL_MODULE_IMPORT_P, but this is not set in cases where the class
is in the global module and matches an existing GM declaration we've
seen (via an include, for example).

This patch fixes this by checking DECL_MODULE_ENTITY_P instead, which is
set on all entities that have been seen from a module import.  We also
use the 'for_mangle' version of get_originating_module so that we don't
treat imported GM entities as attached to the module we imported them
from.  And rename that parameter to something more general.

And dump_module_suffix is another place where we want to treat global module
entities as not coming from a module.

	PR c++/118920

gcc/cp/ChangeLog:

	* name-lookup.cc (lookup_imported_hidden_friend): Check for
	module entity rather than just module import.
	* module.cc (get_originating_module): Rename for_mangle parm to
	global_m1.
	* error.cc (dump_module_suffix): Don't decorate global module decls.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/tpl-friend-17.h: New test.
	* g++.dg/modules/tpl-friend-17_a.C: New test.
	* g++.dg/modules/tpl-friend-17_b.C: New test.

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