Span's PartialEq ignores expn_id, so compare sp.expn_id not sp

We already fixed the comparison at the top of this function.

Author: rprichard

src/libsyntax/diagnostic.rs

@@ -433,7 +433,8 @@ fn emit(dst: &mut EmitterWriter, cm: &codemap::CodeMap, rsp: RenderSpan,
 
     // We cannot check equality directly with COMMAND_LINE_SP
     // since PartialEq is manually implemented to ignore the ExpnId
-    let ss = if sp.expn_id == COMMAND_LINE_EXPN {
+    let is_command_line = sp.expn_id == COMMAND_LINE_EXPN;
+    let ss = if is_command_line {
         "<command line option>".to_string()
     } else {
         cm.span_to_string(sp)
@@ -454,7 +455,7 @@ fn emit(dst: &mut EmitterWriter, cm: &codemap::CodeMap, rsp: RenderSpan,
             try!(highlight_lines(dst, cm, sp, lvl, cm.span_to_lines(sp)));
         }
     }
-    if sp != COMMAND_LINE_SP && rsp.is_full_span() {
+    if !is_command_line && rsp.is_full_span() {
         try!(print_macro_backtrace(dst, cm, sp));
     }
     match code {