Using __builting_assume with Clang makes linker fail to resolve mch::vtblmap<mch::type_switch_info>::update(long)

[solodon4]

This is not a Mach7 bug per se, likely an Apple one, but this tracks the fact that the use of __builtin_assume is currently commented out for clang. This started happening after installing Xcode 7.0.1 but I seem to have the same issue now while trying this on Ubuntu (see build log)

The reduced repro is:

typedef long intptr_t;
namespace mch {

template <typename T> class vtblmap
{
    struct A
    {
        bool is_full() ;
    };
public:
    T& update(intptr_t );
    intptr_t get_vtbl;
    void  get( )
    {
        update(get_vtbl);
    }
    A* descriptor;
};

template <typename T> T& vtblmap<T>::update(intptr_t vtbl)
{
    __builtin_assume(descriptor->is_full())     ; // Comment this out for the linker error to disappear
}

struct type_switch_info ;
class B {
    public:
    static long choose(  )
    {
        vtblmap<type_switch_info> a;
        a.get();
    }
};
}

template<    class S, class T> void  lift_ex2(int , S , T )
{
    mch::B::choose;
}

int b,  c   ;
void  my_g( )
{
    lift_ex2(c,b,my_g);
}