[C++ PATCH] some cleanups

[C++ PATCH] some cleanups

https://gcc.gnu.org/ml/gcc-patches/2019-04/msg01174.html
	* decl.c (duplicate_decls): Add whitespace, move comments into
	conditional blocks.
	* method.c (explain_implicit_non_constexpr): Refactor.
	* pt.c (check_explicit_specialization): Fix indentation.
	* semantics.c (process_outer_var_ref): Reformat.
	(finish_id_expression_1): Use STRIP_TEMPLATE.

From-SVN: r270655