P1091R3 - Extending structured bindings to be more like var decls P1381R1 - Reference capture of structured bindings

	P1091R3 - Extending structured bindings to be more like var decls
	P1381R1 - Reference capture of structured bindings
	* decl.c (cp_maybe_mangle_decomp): Handle TREE_STATIC decls even at
	function scope.
	(cp_finish_decomp): Copy over various decl properties from decl to
	v[i] in the tuple case.
	(grokdeclarator): Allow static, thread_local and __thread for C++2a
	and use pedwarn instead of error for older standard revisions.
	Make other structured binding diagnostic messages more i18n friendly.

	* g++.dg/cpp1z/decomp3.C (test): For static, expect only warning
	instead of error and only for c++17_down.  Add a thread_local test.
	(z2): Add a __thread test.
	* g++.dg/cpp2a/decomp1.C: New test.
	* g++.dg/cpp2a/decomp1-aux.cc: New file.
	* g++.dg/cpp2a/decomp2.C: New test.
	* g++.dg/cpp2a/decomp3.C: New test.

From-SVN: r271730