[Ada] Fix spurious warning on function imported from C in LTO mode

[Eric Botcazou]

We treat System.Address as equivalent to void* for functions imported from C 
and other languages, but the existing implementation was not very robust.

Tested on x86_64-suse-linux, applied on the mainline and 7 branch.


2017-12-13  Eric Botcazou  <ebotca...@adacore.com>

        * gcc-interface/decl.c (gnat_to_gnu_entity): Robustify test for types
        descendant of System.Address.
        (gnat_to_gnu_subprog_type): Likewise.

-- 
Eric Botcazou
Index: gcc-interface/decl.c
===================================================================
--- gcc-interface/decl.c	(revision 255578)
+++ gcc-interface/decl.c	(working copy)
@@ -659,7 +659,7 @@ gnat_to_gnu_entity (Entity_Id gnat_entit
 
 	/* Get the type after elaborating the renamed object.  */
 	if (Has_Foreign_Convention (gnat_entity)
-	    && Is_Descendant_Of_Address (gnat_type))
+	    && Is_Descendant_Of_Address (Underlying_Type (gnat_type)))
 	  gnu_type = ptr_type_node;
 	else
 	  {
@@ -5594,7 +5594,7 @@ gnat_to_gnu_subprog_type (Entity_Id gnat
       /* For foreign convention subprograms, return System.Address as void *
 	 or equivalent.  Note that this comprises GCC builtins.  */
       if (Has_Foreign_Convention (gnat_subprog)
-	  && Is_Descendant_Of_Address (gnat_return_type))
+	  && Is_Descendant_Of_Address (Underlying_Type (gnat_return_type)))
 	gnu_return_type = ptr_type_node;
       else
 	gnu_return_type = gnat_to_gnu_profile_type (gnat_return_type);
@@ -5761,7 +5761,7 @@ gnat_to_gnu_subprog_type (Entity_Id gnat
 	  /* For foreign convention subprograms, pass System.Address as void *
 	     or equivalent.  Note that this comprises GCC builtins.  */
 	  if (Has_Foreign_Convention (gnat_subprog)
-	      && Is_Descendant_Of_Address (gnat_param_type))
+	      && Is_Descendant_Of_Address (Underlying_Type (gnat_param_type)))
 	    gnu_param_type = ptr_type_node;
 	  else
 	    gnu_param_type = gnat_to_gnu_profile_type (gnat_param_type);