Add ability to detect GNU/Hurd when configuring.

Adapted from https://git.hadrons.org/cgit/debian/pkgs/pciutils.git/tree/debian/patches/00-configure-hurd.patch

From e39a3af22501234a91cf28e8c57b45f9379f9101 Mon Sep 17 00:00:00 2001
From: Damien Zammit <damien@zamaudio.com>
Date: Fri, 26 Oct 2018 09:24:04 -0400
Subject: [PATCH 2/2] Add ability to detect GNU/Hurd when configuring

---
 lib/configure |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/lib/configure
+++ b/lib/configure
@@ -25,7 +25,7 @@ if [ -z "$HOST" ] ; then
 		proc=`/usr/sbin/lsdev -C -c processor -S available -F name | head -1`
 		cpu=`/usr/sbin/lsattr -F value -l $proc -a type | sed 's/_.*//'`
 	else
-		cpu=`uname -m | sed 's/^i.86$/i386/;s/^sun4u$/sparc64/;s/^i86pc$/i386/;s/^BePC$/i386/;s/^BeMac$/powerpc/;s/^BeBox$/powerpc/'`
+		cpu=`uname -m | sed 's/^i.86-AT386/i386/;s/^i.86$/i386/;s/^sun4u$/sparc64/;s/^i86pc$/i386/;s/^BePC$/i386/;s/^BeMac$/powerpc/;s/^BeBox$/powerpc/'`
 	fi
 	if [ "$sys" = "DragonFly" ]
 	then
@@ -39,6 +39,10 @@ if [ -z "$HOST" ] ; then
 	then
 		sys=cygwin
 	fi
+	if [ "$sys" = "GNU" ]
+	then
+		sys=gnu
+	fi
 	HOST=${3:-$cpu-$sys}
 fi
 [ -n "$RELEASE" ] && rel="${RELEASE}"
ests.scm'>log</a><a href='/guix/tree/etc/system-tests.scm?id=5ced0440ed74607fb12bf28386fff4c34beac47e'>tree</a><a href='/guix/commit/etc/system-tests.scm?id=5ced0440ed74607fb12bf28386fff4c34beac47e'>commit</a><a href='/guix/diff/etc/system-tests.scm?id=5ced0440ed74607fb12bf28386fff4c34beac47e'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/etc/system-tests.scm'>
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<div class='path'>path: <a href='/guix/log/?id=5ced0440ed74607fb12bf28386fff4c34beac47e'>root</a>/<a href='/guix/log/etc?id=5ced0440ed74607fb12bf28386fff4c34beac47e'>etc</a>/<a href='/guix/log/etc/system-tests.scm?id=5ced0440ed74607fb12bf28386fff4c34beac47e'>system-tests.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/etc/system-tests.scm?id=5ced0440ed74607fb12bf28386fff4c34beac47e&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-03-23 00:06:58 +0100'>2020-03-23</span></td><td><a href='/guix/commit/etc/system-tests.scm?id=8b18f5cb309f670b08ad35df6425f4e9e19d8a82'>tests: Use the same source as ci.guix.gnu.org.</a><span class='msg-avail'>...<span class='msg-tooltip'>* etc/system-tests.scm (system-test-manifest): In 'local-file' call, use
a name that is a function of COMMIT to match what Cuirass does.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-03-05 16:33:38 +0100'>2020-03-05</span></td><td><a href='/guix/commit/etc/system-tests.scm?id=5ec4156bbcaec8337f78411204d59e59e706103b'>tests: Add a manifest for system tests.</a><span class='msg-avail'>...<span class='msg-tooltip'>The manifest can be passed to 'guix build -m', 'guix weather -m', and so
on.  It can also be passed to an installed 'guix' (without
./pre-inst-env), with the exception so far of installation tests.

* build-aux/run-system-tests.scm: Remove.  Move interesting bits move
to...
* etc/system-tests.scm: ... here.  New file.
* Makefile.am (EXTRA_DIST): Remove 'build-aux/run-system-tests.scm' and
add 'etc/system-tests.scm'.
(check-system): Rewrite to run 'guix build -m etc/system-tests.scm'.
</span></span></td><td>Ludovic Courtès</td></tr>