We then set datarootdir to something else later on so that things still
work when configure doesn't set it.
# New autoconf (>= 2.60?) make a configure with a --datarootdir=DIR flag.
# However, in order to support older autoconf's we don't use it.
# datarootdir is set lower down instead.
-# datarootdir = @datarootdir@
+# But, as datadir is defined in terms of datarootdir, we also need to
+# set it to the value (if any) that configure gives it here.
+datarootdir := @datarootdir@
exec_prefix := @exec_prefix@
bindir := @bindir@