Fix handling of configure option --with-xorg-conf-dir

There were two problems:

I accidentally changed the variable name in the AC_ARG_WITH stanza from
configdir to xorgconfigdir, so specifying --with-xorg-conf-dir wouldn't
work correctly. Fix this back to configdir.

If neither --with-xorg-conf-dir nor --prefix is specified on the command
line, the $prefix variable doesn't contain "/usr/local" (the default
prefix) yet at this point but "NONE". So make install would attempt to
install 10-amdgpu.conf in ${DESTDIR}NONE/share/X11/xorg.conf.d/ . Fix
this by leaving ${prefix} verbatim in the default value, to be resolved
by make.

Also print the configdir value along with the values of other similar
configuration variables.

Reported-by: Timo Aaltonen <tjaalton@debian.org>
Reviewed-by: Julien Cristau <jcristau@debian.org>
(Cherry picked from commit aa8a3fa246)

configure.ac

@@ -89,9 +89,9 @@ PKG_CHECK_EXISTS([xorg-server >= 1.16],
 		 [sysconfigdir=""])
 AC_ARG_WITH(xorg-conf-dir,
             AS_HELP_STRING([--with-xorg-conf-dir=DIR],
-                           [Default xorg.conf.d directory [[default=$prefix/share/X11/xorg.conf.d/]]]),
-            [xorgconfdir="$withval"],
-            [xorgconfdir="$prefix/share/X11/xorg.conf.d"])
+                           [Default xorg.conf.d directory [[default=${prefix}/share/X11/xorg.conf.d]]]),
+            [configdir="$withval"],
+            [configdir='${prefix}/share/X11/xorg.conf.d'])
 AC_SUBST(configdir)
 AM_CONDITIONAL(HAS_XORG_CONF_DIR, [test "x$sysconfigdir" != "x"])
 
@@ -279,6 +279,7 @@ echo "        prefix:              $prefix"
 echo "        exec_prefix:         $exec_prefix"
 echo "        libdir:              $libdir"
 echo "        includedir:          $includedir"
+echo "        configdir:           $configdir"
 
 echo ""
 echo "        CFLAGS:              $CFLAGS"