Those willing to reuse archdep-filter elsewhere
will likely have to figure it out from Makefiles
anyway, so probably not worth overdocumenting...

doc/archdep.txt was the reason to look closer,
and some other files needed a bit of facelift
by now too (would be better to do that in sync).

See commit 2d257a42
for details, this just brings those to pkg.in/profiles/
(along with the generic archdep support, of course).

The former ("proper 32-bit x86 package form") has been suggested
by zerg@ quite some time ago but the desired interface wasn't clear
at the moment IIRC; a quiet morning helped me realize that

  ICAClient-preinstall@IA32

is rather more readable than

  ICAClient-preinstall@i586 i586-ICAClient-preinstall@x86_64

so here's the (trivial) implementation; and I actually needed
the latter, @X86 ("any-x86") to mark x86-only packages so

  xorg-drv-intel@X86

is now equivalent to

  xorg-drv-intel@i586 xorg-drv-intel@x86_64

Build process would choke on "unescaped" stuff otherwise,
and these blocks should be blockquotes in the first place.

This is an initial implementation of architecture dependent
contents handling for package lists more or less in the vein
of mkimage-profiles-desktop's one *but* using suffix part to
filter words in or out *not* prefix part to replace it with
a comment marker (thus filtering out lines).

The syntax should be pretty obvious:

  a b@i586 c@x86_64

will get "a b" given ARCH=i586 and "a c" given ARCH=x86_64;
please see doc/archdep.txt for a more elaborate description
and a conversion script.