Link warnings on OSX

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[47/71] LINK ./test_cc
ld: warning: direct access in function '___cxx_global_var_init' from file 'obj/test_cc/flatbuffer_builder_test.o' to global weak symbol 'testing::Test::TearDownTestCase()' from file 'obj/deno_base_test/file_util_test.o' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in function '___cxx_global_var_init' from file 'obj/test_cc/flatbuffer_builder_test.o' to global weak symbol 'testing::Test::SetUpTestCase()' from file 'obj/deno_base_test/file_util_test.o' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in function '___cxx_global_var_init.16' from file 'obj/test_cc/flatbuffer_builder_test.o' to global weak symbol 'testing::Test::TearDownTestCase()' from file 'obj/deno_base_test/file_util_test.o' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in function '___cxx_global_var_init.16' from file 'obj/test_cc/flatbuffer_builder_test.o' to global weak symbol 'testing::Test::SetUpTestCase()' from file 'obj/deno_base_test/file_util_test.o' means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.