[Ada] Fix spurious error on renaming of component of return value

[Eric Botcazou]

This is a long-standing regression present in the compiler: it issues an 
unexpected error on the renaming of a component of the return value of a 
function call, when the return type has dynamic size and the renaming is 
declared at library level.

Tested on x86_64-suse-linux, applied on the mainline.


2016-02-29  Eric Botcazou  <ebotcazou@adacore.com>

	* gcc-interface/ada-tree.h (DECL_RETURN_VALUE_P): New macro.
	* gcc-interface/gigi.h (gigi): Remove useless attribute.
	(gnat_gimplify_expr): Likewise.
	(gnat_to_gnu_external): Declare.
	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Constant>: Factor out
	code dealing with the expression of external constants into...
	Invoke gnat_to_gnu_external instead.
	<E_Variable>: Invoke gnat_to_gnu_external to translate renamed objects
	when not for a definition.  Deal with COMPOUND_EXPR and variables with
	DECL_RETURN_VALUE_P set for renamings and with the case of a dangling
	'reference to a function call in a renaming.  Remove obsolete test and
	adjust associated comment.
	* gcc-interface/trans.c (Call_to_gnu): Set DECL_RETURN_VALUE_P on the
	temporaries created to hold the return value, if any.
	(gnat_to_gnu_external): ...this.  New function.
	* gcc-interface/utils.c (create_var_decl): Detect a constant created
	to hold 'reference to function call.
	* gcc-interface/utils2.c (build_unary_op) <ADDR_EXPR>: Add folding
	for COMPOUND_EXPR in the DECL_RETURN_VALUE_P case.


2016-02-29  Eric Botcazou  <ebotcazou@adacore.com>

	* gnat.dg/renaming8.adb: New test.
	* gnat.dg/renaming8_pkg1.ads: New helper.
	* gnat.dg/renaming8_pkg2.ad[sb]: Likewise.
	* gnat.dg/renaming8_pkg3.ad[sb]: Likewise.


-- 
Eric Botcazou
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