clang拒绝模板`/`运算符,但gnu c接受它

template <class UnitName>
class Quantity 
{
  double value;

public:

  Quantity(double val = 0) : value(val) {}

  Quantity(const Quantity &) {}

  Quantity & operator = (const Quantity &) { return *this; }

  double get_value() const noexcept { return value; }

  operator double() const noexcept { return value; }

  template <class SrcUnit>
  Quantity(const Quantity<SrcUnit> &)
  {
    // here the conversion is done
  }

  template <class SrcUnit>
  Quantity & operator = (const Quantity<SrcUnit> &)
  {
    // here the conversion is done
    return *this;
  }

  template <class TgtUnit> operator TgtUnit() const
  {
    TgtUnit ret;
    // here the conversion is done
    return ret;
  }

  template <class U,class Ur>
  Quantity<Ur> operator / (const Quantity<U> & rhs) const
  {
    return Quantity<Ur>(value / rhs.value);
  }
};

虽然课程要复杂得多,但我认为我提供了足够的信息来描述我的问题：

现在考虑以下代码段：

struct km_h {};
struct Km {};
struct Hour {};

Quantity<km_h> compute_speed(const Quantity<Km> & dist,const Quantity<Hour> & time)
{
  Quantity<km_h> v = dist/time;
  return v;
}

这段代码被gnu c编译器接受,运行良好.调用最后一个模板运算符.

但它被clang编译器(v 3.8.1)拒绝,并带有以下消息：

test-simple.cc:53:26: error: use of overloaded operator '/' is ambiguous (with operand
      types 'const Quantity<Km>' and 'const Quantity<Hour>')
  Quantity<km_h> v = dist/time;
                     ~~~~^~~~~
test-simple.cc:53:26: note: built-in candidate operator/(__int128,unsigned long long)
test-simple.cc:53:26: note: built-in candidate operator/(unsigned long,long double)

所以我的问题是：为什么clang拒绝它？是一个有效的代码？或者gnu c应该拒绝它？

在代码有效的情况下,如何修改它以便clang接受它？