re PR c++/86836 (internal compiler error on structured bindings with shadow parameter on templated function)

	PR c++/86836
	* pt.c (tsubst_expr): For structured bindings, call tsubst_decomp_names
	before tsubst_init, not after it.

	* g++.dg/cpp1z/decomp46.C: New test.

From-SVN: r263391