ifdef cleanup

Get rid of a lot of unnecessary ifdefs that just make the code harder to understand and aren't used on the platforms we support today.

• unifdef ISC
• unifdef sgi
• unifdef __osf__
• unifdef hpux
• unifdef SCO, __SCO__, and __UNIXWARE__
• unifdef sony
• unifdef defined(SVR4) && !defined(sun)
• unifdef __bsdi__
• unifdef BSD < 199103
• unifdef ATHENA
• unifdef INCLUDE_XPRINT_SUPPORT
• unifdef NO_COMPRESS