OpenVMS I64 and OpenVMS x86 only.

    Associates a named or anonymous linkage with a routine name. When
    the compiler sees a CALLS, CALLG, JSB, BSBB, or BSBW instruction
    with the routine name as the target, it will use the associated
    linkage to decide which registers need to be saved and restored
    around the call on Itanium systems and will use the associated
    linkage to decide if the Alpha R0/R1 registers need to be refreshed
    from the hardware return registers.

    Format

      .CALL_LINKAGE  routine_name [,linkage_name] [,input] [,output]

                     [,scratch] [,preserve]