concept checker doesn't compile on gcc because it 'has no linkage'

I've created a concept checking class based on this question whose purpose is to make sure a given class has a static member function called baseUnitConversionFactor. The class compiles and works fine with msvc2013, but it wont compile on gcc 4.9.2 (using -std=c++14) with the error:

error: ‘{anonymous}::UnitsTest_conceptChecker_Test::TestBody()::validUnit::baseUnitConversionFactor’ is not a valid template argument for type ‘double (*)()’ because ‘static double {anonymous}::UnitsTest_conceptChecker_Test::TestBody()::validUnit::baseUnitConversionFactor()’ has no linkage

static std::true_type test(tester<&U::baseUnitConversionFactor>*);

I don't really know what that means, and am much more familiar with writing templates in visual studios (obviously) much more permisive enviornment. Can anyone help figure out what I need to do to fix this?

Concept Checker Class

template <typename T>
struct has_baseUnitConversionFactor
{
    template<double(*)()> struct tester;

    template<typename U>
    static std::true_type test(tester<&U::baseUnitConversionFactor>*);
    template<typename U>
    static std::false_type test(...);

    static const bool value = decltype(test<T>(0))::value;
};

Test which I think causes the error

TEST_F(UnitsTest, conceptChecker)
{
    struct validUnit
    {
        static inline double baseUnitConversionFactor() { return 0.0; }
        typedef void unit_category;
        typedef void base_unit_type;
    };

    EXPECT_TRUE(has_baseUnitConversionFactor<validUnit>::value);
}