consider adding a "common" or "share" sysname

[kaduk]

boojum notes in email that these days, lots of lockers only have perl/shell scripts, with no compiled (i.e., arch-dependent) executables at all. The current state of the art involves giant symlink farms to get things working on all platforms, but we should be able to do better.

"""
I know add falls back to directories corresponding to earlier versions,
so you don't have to have every single thing listed, but it would be
nice if it would fall back to some non-platform specific directory
("common"?) at the end, to avoid the whole "must supply a dozen
different ways to reach the same platform-independent program" mess.
"""

[andersk]

For lockers with both binaries and scripts, it would be a little more convenient if “common”/“share” were always added to the path after the platform directory, even if a platform directory exists.

(That’s not entirely consistent with the bin → arch/@sys/bin fiction, but it wasn’t a very good fiction to begin with.)

[achernya]

We should about names here -- "common" is probably not ideal despite being in use. I think we may want "noarch".

[jdreed]

achernya suggests we do this in utopic so we have time to crash-and-burn before the next cluster release. I concur.

[jdreed]

Discussed at release-team. arch/noarch/bin at the end of the PATH is the way to go. (and MANPATH, etc). We need to think a bit about how to incorporate this into athdir's idea that arch dependency and independency are mutually exclusive. I think we can also rip out the machtypebin compatibility at this point. It was always a bad idea, worked terribly on Linux 2.4 and later (because libc). Along with the fix for #1540, we can switch "Using compatibility" to "This locker is too old".