Given an invocation context block and SSE (Streaming SIMD
    Extensions) register index such that 0 <= index < 16, copy the
    register value to xmm_copy. For example, an index value of 4
    fetches the value, which represents the contents of xmm4.
    LIB$X86_GET_MMX returns failure status if there is no
    corresponding XSAVE area in the invo_context or if the index
    represents a register or register set not saved in the XSAVE
    area.

    Format
      LIB$X86_GET_XMM (invo_context, index, xmm_copy)