updated E0395 to new error format

Author: clementmiao

src/librustc_mir/transform/qualify_consts.rs

@@ -678,9 +678,14 @@ impl<'a, 'tcx> Visitor<'tcx> for Qualifier<'a, 'tcx, 'tcx> {
 
                     self.add(Qualif::NOT_CONST);
                     if self.mode != Mode::Fn {
-                        span_err!(self.tcx.sess, self.span, E0395,
-                                  "raw pointers cannot be compared in {}s",
-                                  self.mode);
+                        struct_span_err!(
+                            self.tcx.sess, self.span, E0395,
+                            "raw pointers cannot be compared in {}s",
+                            self.mode)
+                        .span_label(
+                            self.span,
+                            &format!("comparing raw pointers in static"))
+                        .emit();
                     }
                 }
             }

src/test/compile-fail/E0395.rs

@@ -12,6 +12,6 @@ static FOO: i32 = 42;
 static BAR: i32 = 42;
 
 static BAZ: bool = { (&FOO as *const i32) == (&BAR as *const i32) }; //~ ERROR E0395
-
+                   //~| NOTE comparing raw pointers in static
 fn main() {
 }

src/test/compile-fail/issue-25826.rs

@@ -12,5 +12,6 @@ fn id<T>(t: T) -> T { t }
 fn main() {
     const A: bool = id::<u8> as *const () < id::<u16> as *const ();
     //~^ ERROR raw pointers cannot be compared in constants [E0395]
+    //~^^ NOTE comparing raw pointers in static
     println!("{}", A);
 }