PR c++/67012
	PR c++/86942
	* decl.c (grokdeclarator): Disallow functions with trailing return
        type with decltype(auto) as its type.  Also check the function if
        it's inner declarator doesn't exist

	* g++.dg/cpp0x/auto52.C: New test.
	* g++.dg/cpp1y/auto-fn52.C: New test.
	* g++.dg/cpp1y/auto-fn53.C: New test.
	* g++.dg/cpp1y/auto-fn54.C: New test.

From-SVN: r263836