Fix test compilation with exa.h in configure when using glibc 2.20.
Inspired by a patch by Peter Hutterer <peter.hutterer@who-t.net>.
See <https://raw.githubusercontent.com/openembedded/oe-core/master/meta/recipes-graphics/xorg-driver/xf86-input-synaptics/always_include_xorg_server.h.patch>.

--- xf86-video-mach64-6.9.4/configure.~1~	2012-12-20 01:16:10.000000000 -0500
+++ xf86-video-mach64-6.9.4/configure	2014-12-19 02:48:18.040097554 -0500
@@ -18370,7 +18370,9 @@
 
         SAVE_CPPFLAGS="$CPPFLAGS"
         CPPFLAGS="$CPPFLAGS $XORG_CFLAGS"
-        ac_fn_c_check_header_mongrel "$LINENO" "exa.h" "ac_cv_header_exa_h" "$ac_includes_default"
+        ac_fn_c_check_header_mongrel "$LINENO" "exa.h" "ac_cv_header_exa_h" "$ac_includes_default
+#include <xorg-server.h>
+"
 if test "x$ac_cv_header_exa_h" = xyes; then :
   have_exa_h="yes"
 else
submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9'>refs</a><a class='active' href='/guix/log/gnu/services/dbus.scm'>log</a><a href='/guix/tree/gnu/services/dbus.scm?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9'>tree</a><a href='/guix/commit/gnu/services/dbus.scm?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9'>commit</a><a href='/guix/diff/gnu/services/dbus.scm?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/services/dbus.scm'>
<input type='hidden' name='id' value='7294cbecdd89156c6c651f30ad4c29ad051b46d9'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9'>root</a>/<a href='/guix/log/gnu?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9'>gnu</a>/<a href='/guix/log/gnu/services?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9'>services</a>/<a href='/guix/log/gnu/services/dbus.scm?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9'>dbus.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/gnu/services/dbus.scm?id=7294cbecdd89156c6c651f30ad4c29ad051b46d9&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-05-08 16:30:50 +0200'>2020-05-08</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=dd0804c67e99914eecc471fdb92f4220425a1cbc'>services: Add descriptions.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-11-13 23:26:36 +0100'>2019-11-13</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=1f8ca28b9e517f73d1a640dbbd11eadbf35b885b'>services: dbus: Simplify 'dbus-uuidgen' invocation.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-11-13 23:26:36 +0100'>2019-11-13</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=7462a1de22636dde24d56225c67bb3c10118b698'>services: dbus: Log to syslog.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-11-13 23:26:36 +0100'>2019-11-13</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=a01d2e300abf8721866c8d1f984b0db90d192f9d'>services: dbus: Add description.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-11-02 00:12:19 +0100'>2019-11-02</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=27727b18b8597f7c6fd99adc7797c555aa1c92e9'>services: dbus: Remove non-existent directories from 'system-local.conf'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-11-02 00:12:19 +0100'>2019-11-02</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=33f9778bc83086837b99e5c5e99cd514cb0d154e'>services: dbus: Include each service's "share/dbus-1/system.d".</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-04-05 15:39:35 +0200'>2019-04-05</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=aa071ca049c4324c790b3364e6c4c8e886d26a9e'>services: dbus: 'wrapped-dbus-service' accepts a list of variables.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-04-05 15:39:35 +0200'>2019-04-05</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=b68f65007f50175a68cd174ad7c1036cf622556d'>services: dbus: Add 'wrapped-dbus-service'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-08 23:21:59 +0100'>2019-03-08</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=d429878daf3e3eb21660ed80934b1d4b0603f6e1'>activation: Shared system home directories are now 555 and root-owned.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-05-20 21:42:33 +0300'>2018-05-20</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=6a2b906565b677d62210d69d418ce150c202931b'>services: dbus: Search more directories for '.service' files.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>