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 __osf__
• unifdef AIXV3
• unifdef ultrix
• unifdef __UNIXOS2__
• unifdef hpux
• unifdef sgi
• unifdef __sgi
• unifdef __sgi_not_xconsortium
• unifdef __vax__
• unifdef __uxp__
• unifdef __QNX__