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
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<tr><td><span title='2018-08-20 21:43:56 -0700'>2018-08-20</span></td><td><a href='/guix/commit/gnu/services/security-token.scm?id=6fb6ac6857df31c55a640eead2a5f79edd7dab14'>gnu: services: Fix pcscd activation bug.</a><span class='msg-avail'>...<span class='msg-tooltip'>Fixes: &lt;https://bugs.gnu.org/32478&gt;.

* gnu/services/security-token.scm (pcscd-activation): Idempotently create the
/var/lib/pcsc symlink so that it does not fail when it already exists.
</span></span></td><td>Chris Marusich</td></tr>
<tr><td><span title='2018-08-16 02:46:27 +0530'>2018-08-16</span></td><td><a href='/guix/commit/gnu/services/security-token.scm?id=de30205ba0f63eb987097a9f47b6e4fd38cd9044'>gnu: services: Add pcscd service.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/security-token.scm: New file.
* gnu/tests/security-token.scm: New file.
* gnu/local.mk (GNU_SYSTEM_MODULES): Register new files.
* doc/guix.texi (Miscellaneous Services): Document the service.
</span></span></td><td>Arun Isaac</td></tr>