[bazel] Add missing dependency for 5d2a710

Author: d0k

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

@@ -26,6 +26,7 @@ cc_test(
         "//llvm:Core",
         "//llvm:Support",
         "//llvm:TestingSupport",
+        "//llvm:config",
         "//third-party/unittest:gmock",
         "//third-party/unittest:gtest",
         "//third-party/unittest:gtest_main",