c++/modules: Fix merge of TLS init functions [PR120363]

c++/modules: Fix merge of TLS init functions [PR120363]

The PR notes that we missed setting DECL_CONTEXT on the TLS init
function; we missed this initially because this function is not created
in header units, only named modules.

I also noticed that 'DECL_CONTEXT (fn) = DECL_CONTEXT (var)' was
incorrect: for class members, this ends up having the modules merging
machinery treat the decl as a member function, which breaks when
attempting to dedup against an existing completed class type.  Instead
we can just use the global_namespace as the context, because the name of
the function is already mangled appropriately so that we'll match the
correct duplicates.

	PR c++/120363

gcc/cp/ChangeLog:

	* decl2.cc (get_tls_init_fn): Set context as global_namespace.
	(get_tls_wrapper_fn): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr113292_a.H: Move to...
	* g++.dg/modules/tls-1_a.H: ...here.
	* g++.dg/modules/pr113292_b.C: Move to...
	* g++.dg/modules/tls-1_b.C: ...here.
	* g++.dg/modules/pr113292_c.C: Move to...
	* g++.dg/modules/tls-1_c.C: ...here.
	* g++.dg/modules/tls-2_a.C: New test.
	* g++.dg/modules/tls-2_b.C: New test.
	* g++.dg/modules/tls-2_c.C: New test.
	* g++.dg/modules/tls-3.h: New test.
	* g++.dg/modules/tls-3_a.H: New test.
	* g++.dg/modules/tls-3_b.C: New test.

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