C++ code that clang++ does not accept but g++ does

stack.cc

#include <cstdlib>

struct Entry {
  unsigned char key;
  std::size_t value;
};

template <typename EntryT>
class Klass {
 public:
  static std::size_t size(std::size_t size) {
    return size * sizeof(Entry);
  }

  Klass() {}
  ~Klass() {}
};

int main() {
  char mem[Klass<Entry>::size(10)];
  return 0;
}