Depends-on:
stdio
-open [test $REPLACE_POPEN = 1]
+open [test $HAVE_POPEN = 0 || test $REPLACE_POPEN = 1]
configure.ac:
gl_FUNC_POPEN
-if test $REPLACE_POPEN = 1; then
+if test $HAVE_POPEN = 0 || test $REPLACE_POPEN = 1; then
AC_LIBOBJ([popen])
gl_PREREQ_POPEN
fi