need better OS classes on Irix

[Dave Love]

A system which is actually Irix 6.5.20m gives me these classes:

Additional hard class defined as: 32_bit
Additional hard class defined as: irix_6_5
Additional hard class defined as: irix_ip22
Additional hard class defined as: irix_ip22_6_5
Additional hard class defined as: mips
Additional hard class defined as: irix_ip22_6_5_04091957

and 6.5.19m gives:

Additional hard class defined as: 32_bit
Additional hard class defined as: irix64_6_5
Additional hard class defined as: irix64_ip27
Additional hard class defined as: irix64_ip27_6_5
Additional hard class defined as: mips
Additional hard class defined as: irix64_ip27_6_5_01100304

The trouble is, I can't use these to distinguish the two versions on
arbitrary systems for the purposes of applying patches, say.  The
`01100304' presumably corresponds to the `.19m' in uname output:

$ uname -sR
IRIX64 6.5 6.5.19m

but the class is conflated with the SGI board type (`ip27' &c).

I can't quickly follow how these get defined.  What code would I have
to look at to provide a patch defining a class with the detailed OS
version but not the board type?  (Something like
`irix64_mips_6_5_01100304' would be fine, corresponding to Tru64, for
instance, which doesn't have architecture details involved:
`osf1_alpha_V5_1_2650'.)

Obviously I can match the result of running uname a few times, so it's
not a blocking problem, but it would be helpful to address it.