Initializes an invocation context block that the user has
    already allocated (on the stack, or from heap, or other
    storage). Use this routine as an alternative to
    LIB$X86_CREATE_INVO_CONTEXT, which both allocates and
    initializes an invocation context block.

    Format
      LIB$X86_INIT_INVO_CONTEXT (invo_context, invo_version [,
      cache_unwind_flag])