[bazel][clang] Add missing dependency for 6e31714

Author: d0k

utils/bazel/llvm-project-overlay/clang/unittests/BUILD.bazel

@@ -110,6 +110,7 @@ cc_test(
         "//clang:ast",
         "//clang:ast_matchers",
         "//clang:basic",
+        "//clang:frontend",
         "//clang:lex",
         "//clang:parse",
         "//clang:tooling",