[Ada] Fix internal error on problematic renaming

[Eric Botcazou]

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.

Tested on x86-64/Linux, applied on the mainline.


2020-05-25  Eric Botcazou  <ebotcazou@adacore.com>

	* 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.


2020-05-25  Eric Botcazou  <ebotcazou@adacore.com>

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

-- 
Eric Botcazou
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