c++: Ensure DECL_CONTEXT is set for temporary vars [PR114005]

Modules streaming requires DECL_CONTEXT to be set for anything streamed.
This patch ensures that 'create_temporary_var' does set a DECL_CONTEXT
for these variables (such as the backing storage for initializer_lists)
even if not inside a function declaration.

	PR c++/114005

gcc/cp/ChangeLog:

	* init.cc (create_temporary_var): Use current_scope instead of
	current_function_decl.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/pr114005_a.C: New test.
	* g++.dg/modules/pr114005_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>