+# into makefiles. And do it only for sed versions 4.2 or newer,
+# because "sed --posix" is buggy in GNU sed 4.1.5, see
+# <http://lists.gnu.org/archive/html/bug-gnulib/2009-02/msg00225.html>.
+if (alias) > /dev/null 2>&1 \
+ && echo | sed --posix -e d >/dev/null 2>&1 \
+ && case `sed --version | sed -e 's/^[^0-9]*//' -e 1q` in \
+ [1-3]* | 4.[01]*) false;; \
+ *) true;; \
+ esac \
+ ; then