Enable cppcoreguidelines-special-member-functions check

We only had one violation of this, which was in a test case, so fix that
test case, and enable this check.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I1288a6d51593bb6d4c3a73dabaa566bf29474b5e
diff --git a/.clang-tidy b/.clang-tidy
index 001c11a..9386f6a 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -189,6 +189,7 @@
 clang-analyzer-webkit.RefCntblBaseVirtualDtor,
 cppcoreguidelines-avoid-c-arrays,
 cppcoreguidelines-init-variables,
+cppcoreguidelines-special-member-functions,
 misc-misplaced-const,
 misc-no-recursion,
 misc-redundant-expression,