c++ modules: lazy loading from within template [PR99377]

c++ modules: lazy loading from within template [PR99377]

Here when lazily loading the binding for f due to its first use from the
template g, processing_template_decl is set which causes the call to
note_vague_linkage_fn from module_state::read_cluster to have no effect,
and thus we never push f onto deferred_fns and end up never emitting its
definition despite needing it.

The behavior of the lazy loading machinery shouldn't be sensitive to
whether we're inside a template, so to that end this patch makes us
clear processing_template_decl in the entrypoints lazy_load_binding and
lazy_load_pendings.

	PR c++/99377

gcc/cp/ChangeLog:

	* module.cc (lazy_load_binding): Clear processing_template_decl.
	(lazy_load_pendings): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr99377-2_a.C: New test.
	* g++.dg/modules/pr99377-2_b.C: New test.