rustc_lint: Prevent multiple 'lint ignored' lints

Prevent multiple 'ignored unless specified at crate level' lints. The
multiplication happens because we run the same lint three times:
* In BuiltinCombinedEarlyLintPass
* In BuiltinCombinedPreExpansionLintPass
* In shallow_lint_levels_on

Only run the lint one time by checking the `lint_added_lints` bool.

compiler/rustc_lint/src/levels.rs

@@ -1029,7 +1029,7 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
             }
         }
 
-        if !is_crate_node {
+        if self.lint_added_lints && !is_crate_node {
             for (id, &(level, ref src)) in self.current_specs().iter() {
                 if !id.lint.crate_level_only {
                     continue;