message: fix ENOKI_{UN}LIKELY macros for MSVC
diff: # define ENOKI_NOUNROLL
  # define ENOKI_IVDEP __pragma(loop(ivdep))
  # define ENOKI_PACK
  -# define ENOKI_LIKELY(x)
  -# define ENOKI_UNLIKELY(x)
  +# define ENOKI_LIKELY(x) x
  +# define ENOKI_UNLIKELY(x) x
  #else
  # define ENOKI_NOINLINE __attribute__ ((noinline))
  # define ENOKI_INLINE __attribute__ ((always_inline)) inline
  