Fix internal error on problematic renaming

Fix internal error on problematic renaming

This is an internal renaming generated for a generalized loop iteration
made on a tagged record type with predicate, and gigi cannot use the most
efficient way of implementing renamings because the renamed object is an
expression with a non-empty Actions list.

gcc/ada/ChangeLog
	* gcc-interface/decl.c (gnat_to_gnu_entity): Add new local variable
	and use it throughout the function.
	<E_Variable>: Rename local variable and adjust accordingly.  In the
	case of a renaming, materialize the entity if the renamed object is
	an N_Expression_With_Actions node.
	<E_Procedure>: Use Alias accessor function consistently.

gcc/testsuite/ChangeLog
	* gnat.dg/renaming16.adb: New test.
	* gnat.dg/renaming16_pkg.ads: New helper.