Bug 1540769 - Enable readability-redundant-preprocessor r=andi

Differential Revision: https://phabricator.services.mozilla.com/D25630

--HG--
extra : moz-landing-system : lando

tools/clang-tidy/config.yaml

@@ -134,6 +134,7 @@ clang_checkers:
   - name: readability-misleading-indentation
   - name: readability-non-const-parameter
   - name: readability-redundant-control-flow
+  - name: readability-redundant-preprocessor
   - name: readability-redundant-smartptr-get
   - name: readability-redundant-string-cstr
   - name: readability-redundant-string-init