Update clang, re-enable checker, fix issues it flags

services/files/c/tests/mojio_test_base.h

Index: services/files/c/tests/mojio_test_base.h
diff --git a/services/files/c/tests/mojio_test_base.h b/services/files/c/tests/mojio_test_base.h
index 61404ab2ad16905e4b1ab28c24f7d0ab83a958ab..572fee73703daa49b4e351584a5e305d421c4022 100644
--- a/services/files/c/tests/mojio_test_base.h
+++ b/services/files/c/tests/mojio_test_base.h
@@ -19,24 +19,8 @@ class MojioTestBase : public MojioImplTestBase {
   MojioTestBase() {}
   ~MojioTestBase() override {}
 
-  void SetUp() override {
-    MojioImplTestBase::SetUp();
-
-    // Explicitly set up the singletons.
-    MOJO_CHECK(singletons::GetErrnoImpl());
-    MOJO_CHECK(singletons::GetFDTable());
-    singletons::SetCurrentWorkingDirectory(directory().Pass());
-    MOJO_CHECK(singletons::GetCurrentWorkingDirectory());
-  }
-
-  void TearDown() override {
-    // Explicitly tear down the singletons.
-    singletons::ResetCurrentWorkingDirectory();
-    singletons::ResetFDTable();
-    singletons::ResetErrnoImpl();
-
-    MojioImplTestBase::TearDown();
-  }
+  void SetUp() override;
+  void TearDown() override;
 
  private:
   MOJO_DISALLOW_COPY_AND_ASSIGN(MojioTestBase);