Plugin multimeter: fix compilation error in AIX.

The plugin multimeter is build by default,  in AIX when you compile in 64 bit you get the error:

    Target "all-am" is up to date.
      CC     multimeter.lo
    multimeter.c: In function 'multimeter_init':
    multimeter.c:173:4: error: overflow in implicit constant conversion [-Werror=overflow]
    cc1: all warnings being treated as errors
    make: 1254-004 The error code from the last command is 1.

The  TIOCMBIC is defined:

    sys/ioctl.h:#define   TIOCMBIC        _IOW('t', 107, int)     /* bic modem bits */

and the other defines:

    sys/stropts.h:#define _IOW(x,y,t)     (_IOC_IN|((sizeof(t)&_IOCPARM_MASK)<<16)|(x<<8)|y)
    sys/stropts.h:#define _IOC_IN          0x80000000      /* copy in parameters */
    sys/stropts.h:#define _IOCPARM_MASK    0x7f

in /usr/include/sys/ioctl.h more than a half have a cast to int, for example:

    #define SIOCADDMTU      (int)_IOW('i',112, int) /* add mtu  */
    #define SIOCDELMTU      (int)_IOW('i',113, int) /* delete mtu */
    #define SIOCIF_ATM_UBR          (int)_IOW('i',120,struct ifreq)  /* set ubr rate */
    #define SIOCIF_ATM_SNMPARP      (int)_IOW('i',121,struct ifreq)  /* atm snmp arp */
    #define SIOCIF_ATM_IDLE         (int)_IOW('i',122,struct ifreq)  /* set idle time */
    #define   TIOCMBIC        _IOW('t', 107, int)     /* bic modem bits */

If you compile in AIX collectd in 32 bits you will not get the error.

Other option is to disable the build of multimeter in AIX.