configure.ac: also print ${datarootdir} in summary

It goes something like:

    ${XLOCALEDIR} ->
    ${datarootdir}/locale/X11 ->
    ${prefix}/share/locale/X11 ->
    /usr/share/locale/X11

But AC_MSG_RESULT only performs one substitution. Instead of starting to
expand this stuff manually, just print datarootdir so all the pieces are
there.

Signed-off-by: Ran Benita <ran234@gmail.com>

configure.ac

@@ -209,6 +209,7 @@ AC_MSG_RESULT([
         prefix:                  ${prefix}
         includedir:              ${includedir}
         lib dir:                 ${libdir}
+        datarootdir:             ${datarootdir}
         XKB config root:         ${XKBCONFIGROOT}
         X11 locale root:         ${XLOCALEDIR}
 ])