config.guess Linux overhaul

[Ben Elliston]

It's that time again.  The config.guess script is losing on GNU/Linux and
this time, I'm going to fix it.

Background: on many GNU/Linux systems, config.guess uses the output of `ld
--help' to determine which architecture, object file format and C library
version the build system uses.  The script loses because it assumes that the
primary configuration will appear first in the `supported emulations:'
printed by ld(1).

This is flawed because a) this is not a meaningful constraint and b) some
distributions, such as Caldera OpenLinux, provide a linker that has support
for linking in many, many environments (like coff-z8k, if that grabs you!).

Instead, I am seeking to replace this cruft with a cleaner and more portable
alternative.  After much deliberation, the best I have come up with is to
use file(1) from GNU fileutils, which is *very* likely to be present on
every GNU/Linux system.  The one drawback here is that it doesn't help me
determine the version of libc installed on the system--and there may even be
multiple versions.  Which is the "primary"?  The one that the current C
compiler will link against?

Comments, please.

Ben