Assembly and disassembly of large types

The MMA functions in this section construct __vector_pair and __vector_quad objects from 128-bit vectors, and destruct them into such vectors.

The __builtin_mma_disassemble_acc and __builtin_vsx_disassemble_pair functions place the results into arrays of vectors using natural element order. The __builtin_mma_build_acc and __builtin_vsx_build_pair functions treat the vector input arguments as if they formed an array of vectors, with the first vector argument being array element 0 in natural element order, the second vector argument being array element 1, and so forth.