[C++ Patch] Improve handle_nodiscard_attribute location

[Paolo Carlini]

Hi,

it seems we can easily improve this location by using 
DECL_SOURCE_LOCATION in the standard way. Tested x86_64-linux.

Thanks, Paolo.

//////////////////

/cp
2019-01-02  Paolo Carlini  <paolo.carl...@oracle.com>

        * tree.c (handle_nodiscard_attribute): Improve warning location.

/testsuite
2019-01-02  Paolo Carlini  <paolo.carl...@oracle.com>

        * g++.dg/cpp1z/nodiscard3.C: Test locations too.
Index: cp/tree.c
===================================================================
--- cp/tree.c   (revision 267507)
+++ cp/tree.c   (working copy)
@@ -4372,8 +4372,9 @@ handle_nodiscard_attribute (tree *node, tree name,
   if (TREE_CODE (*node) == FUNCTION_DECL)
     {
       if (VOID_TYPE_P (TREE_TYPE (TREE_TYPE (*node))))
-       warning (OPT_Wattributes, "%qE attribute applied to %qD with void "
-                "return type", name, *node);
+       warning_at (DECL_SOURCE_LOCATION (*node),
+                   OPT_Wattributes, "%qE attribute applied to %qD with void "
+                   "return type", name, *node);
     }
   else if (OVERLOAD_TYPE_P (*node))
     /* OK */;
Index: testsuite/g++.dg/cpp1z/nodiscard3.C
===================================================================
--- testsuite/g++.dg/cpp1z/nodiscard3.C (revision 267507)
+++ testsuite/g++.dg/cpp1z/nodiscard3.C (working copy)
@@ -13,8 +13,8 @@ typedef struct { char big[1024]; fnt fn; } C;
 struct [[nodiscard]] D { int i; D(); ~D(); };
 
 WUR E check1 (void);
-WUR void check2 (void); /* { dg-warning "nodiscard" } */
-WUR int foo;           /* { dg-warning "nodiscard" } */
+WUR void check2 (void); /* { dg-warning "10:.nodiscard." } */
+WUR int foo;           /* { dg-warning "9:.nodiscard." } */
 int bar (void);
 WURAI E check3 (void) { return (E)bar (); }
 WUR A check4 (void);