message: Add MFEM_DEVICE_COMPILE to backends.hpp
diff: #endif
  #endif
  +#if (defined(__CUDA_ARCH__) || defined(__HIP_DEVICE_COMPILE__))
  +#define MFEM_DEVICE_COMPILE
  +#endif
  +
  #if !(defined(MFEM_USE_CUDA) || defined(MFEM_USE_HIP))
  #define MFEM_DEVICE
  #define MFEM_LAMBDA
  