d: Set TYPE_ARTIFICIAL on internal TypeInfo types

Prevents them from triggering warnings when compiling with `-Wpadded'.

gcc/d/ChangeLog:

	* typeinfo.cc (make_internal_typeinfo): Set TYPE_ARTIFICIAL.

gcc/testsuite/ChangeLog:

	* gdc.dg/Wpadded.d: New test.

gcc/d/typeinfo.cc

@@ -180,6 +180,7 @@ make_internal_typeinfo (tinfo_kind tk, Identifier *ident, ...)
 
   /* Create the TypeInfo type.  */
   tree type = make_node (RECORD_TYPE);
+  TYPE_ARTIFICIAL (type) = 1;
   finish_builtin_struct (type, ident->toChars (), fields, NULL_TREE);
 
   tinfo_types[tk] = type;

gcc/testsuite/gdc.dg/Wpadded.d

@@ -0,0 +1,4 @@
+// { dg-do compile }
+// { dg-options "-Wpadded" }
+
+class EmptyClass { }