Use datarootdir instead of datadir

datarootdir should be used instead of datadir.

https://www.gnu.org/software/autoconf/manual/autoconf-2.69/html_node/Changed-Directory-Variables.html

m4macros/Makefile.am

@@ -4,7 +4,7 @@
 # Written for Xfce by Benedikt Meurer <benny@xfce.org>.
 #
 
-macrodir = $(datadir)/aclocal
+macrodir = $(datarootdir)/aclocal
 macro_DATA =								\
 	xdt-depends.m4							\
 	xdt-features.m4							\

m4macros/xdt-i18n.m4

@@ -62,7 +62,7 @@ AC_DEFUN([XDT_I18N],
     if test x"$CATOBJEXT" = x".mo"; then
       localedir=$libdir/locale
     else
-      localedir=$datadir/locale
+      localedir=$datarootdir/locale
     fi
   ])
   AC_MSG_RESULT([$localedir])