+ dnl This ifdef is necessary to avoid an error "missing file lib/stdio-write.c"
+ dnl "expected source file, required through AC_LIBSOURCES, not found". It is
+ dnl also an optimization, to avoid performing a configure check whose result
+ dnl is not used. But it does not make the test of GNULIB_STDIO_H_NONBLOCKING
+ dnl or GNULIB_NONBLOCKING redundant.