[Ada] Do not give warnings for compiler-generated entities by default

[Ada] Do not give warnings for compiler-generated entities by default

[Pierre-Marie de Rodat]

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The rationale is that these entities are almost always the result of
expansion activities in the front-end, over which the user has very
limited control.  These warnings can be restored by means of -gnatD.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* gcc-interface/utils.cc (gnat_pushdecl): Also set TREE_NO_WARNING
	on the decl if Comes_From_Source is false for the associated node.

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diff --git a/gcc/ada/gcc-interface/utils.cc b/gcc/ada/gcc-interface/utils.cc
--- a/gcc/ada/gcc-interface/utils.cc
+++ b/gcc/ada/gcc-interface/utils.cc
@@ -852,8 +852,11 @@ gnat_pushdecl (tree decl, Node_Id gnat_node)
   if (!deferred_decl_context)
     DECL_CONTEXT (decl) = context;
 
-  suppress_warning (decl, all_warnings,
-		    No (gnat_node) || Warnings_Off (gnat_node));
+  /* Disable warnings for compiler-generated entities or explicit request.  */
+  if (No (gnat_node)
+      || !Comes_From_Source (gnat_node)
+      || Warnings_Off (gnat_node))
+    suppress_warning (decl);
 
   /* Set the location of DECL and emit a declaration for it.  */
   if (Present (gnat_node) && !renaming_from_instantiation_p (gnat_node))