Work around two -Werror warning issues in googletest, which have been
solved upstream in the mean time.

The first issue is because one of googletest's generated headers contain
classes with a user-declared copy assignment operator, but rely on the
generation by the compiler of an implicit copy constructor, which is now
deprecated:

/usr/obj/usr/src/amd64.amd64/tmp/usr/include/private/gtest/internal/gtest-param-util-generated.h:5284:8: error: definition of implicit copy constructor for 'CartesianProductHolder3<testing::internal::ParamGenerator<bool>, testing::internal::ValueArray3<int, int, int>, testing::internal::ValueArray4<cache_mode, cache_mode, cache_mode, cache_mode> >' is deprecated because it has a user-declared copy assignment operator [-Werror,-Wdeprecated-copy]

void operator=(const CartesianProductHolder3& other);
     ^

/usr/obj/usr/src/amd64.amd64/tmp/usr/include/private/gtest/gtest-param-test.h:1277:10: note: in implicit copy constructor for 'testing::internal::CartesianProductHolder3<testing::internal::ParamGenerator<bool>, testing::internal::ValueArray3<int, int, int>, testing::internal::ValueArray4<cache_mode, cache_mode, cache_mode, cache_mode> >' first required here

return internal::CartesianProductHolder3<Generator1, Generator2, Generator3>(
       ^

/usr/src/tests/sys/fs/fusefs/io.cc:534:2: note: in instantiation of function template specialization 'testing::Combine<testing::internal::ParamGenerator<bool>, testing::internal::ValueArray3<int, int, int>, testing::internal::ValueArray4<cache_mode, cache_mode, cache_mode, cache_mode> >' requested here

Combine(Bool(),                                 /* async read */
^

For now, silence the warning using -Wno-deprecated-copy.

The second issue is because one of the googlemock test programs attempts
to use "unsigned wchar_t" and "signed wchar_t", which are non-standard
and at best, hazily defined:

contrib/googletest/googlemock/test/gmock-actions_test.cc:111:37: error: 'wchar_t' cannot be signed or unsigned [-Wsigned-unsigned-wchar]

EXPECT_EQ(0U, BuiltInDefaultValue<unsigned wchar_t>::Get());
                                  ^

contrib/googletest/googlemock/test/gmock-actions_test.cc:112:36: error: 'wchar_t' cannot be signed or unsigned [-Wsigned-unsigned-wchar]

EXPECT_EQ(0, BuiltInDefaultValue<signed wchar_t>::Get());
                                 ^

For now, silence the warning using -Wno-signed-unsigned-wchar.

MFC after: 3 days