[PR c++/84733] ICE in check-local-shadow

https://gcc.gnu.org/ml/gcc-patches/2018-03/msg00425.html
	PR c++/84733
	* name-lookup.c (do_pushdecl_with_scope): Only clear
	current_function_decl when pushing a non-class (i.e. namespace)
	scope.

From-SVN: r258383