message: switch StaticArrayImpl constructor/assignment operator to default
  This fixes a calling convention regression where GCC and Clang were
  unable to pass Enoki arguments using registers
diff: @@ -1703,12 +1703,9 @@ ENOKI_NOINLINE std::ostream &operator<<(std::ostream &os,
  using Base::derived; \
  Register m; \
  ENOKI_TRIVIAL_CONSTRUCTOR(Value_) \
  - StaticArrayImpl(const StaticArrayImpl &a) : m(a.m) { } \
  ENOKI_INLINE StaticArrayImpl(Register value) : m(value) { } \
  - StaticArrayImpl &operator=(const StaticArrayImpl &a) { \
  - m = a.m; \
  - return *this; \
  - } \
  + StaticArrayImpl(const StaticArrayImpl &a) = default; \
  + StaticArrayImpl &operator=(const StaticArrayImpl &a) = default; \
  ENOKI_INLINE Value &coeff(size_t i) { return ((Value *) &m)[i]; } \
  ENOKI_INLINE const Value &coeff(size_t i) const { \
  return ((const Value *) &m)[i]; \
  