GCC/clang warning incompatibility with unused private member variables

[Jonathan Wakely]

Here's another #pragma solution to your problem:

class Test {
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wpragmas" // so GCC ignores next line
# pragma GCC diagnostic ignored "-Wunused-private-field"
     int a_;
# pragma GCC diagnostic pop
     void b() {};
};

First tell GCC not to warn about the warning option that it doesn't
recognize, then use that option to tell clang to not warn about the
unused member.