This routine maps a module, with the given txtrfa, into process
    P2 memory space and returns the virtual address where the module
    is mapped and the module size.

    Unlike other LBR services that use RMS services, LBR$MAP_MODULE
    also uses system services. Because of this, the secondary status
    for error returns is placed in LBR$$GL_SUBSTS. Use this secondary
    status to find additional status when an error is returned.