Here's a fully compiled version, principles applied in modifying the code has been mentioned in the links above:
ssamp2 = Compile[{{n, _Integer}, {nd, _Integer}},
Partition[Function[xyzw, {{xyzw[[1]] + I xyzw[[2]],
-xyzw[[3]] + I xyzw[[4]]},
{xyzw[[3]] + I xyzw[[4]],
xyzw[[1]] - I xyzw[[2]]}}]@#/Sqrt@Total[#^2] & /@
Flatten[Transpose@RandomVariate[NormalDistribution[0RandomVariate[NormalDistribution[0, 1], {n, nd, 4}], 1], n]]