Within glibc, it is always safe to call fflush (stdout), even if stdout has been
previously closed.  However, POSIX does not require this guarantee, and there
are other platforms where attempting a flush in this situation causes a SIGSEGV:

http://thread.gmane.org/gmane.comp.lib.gnulib.bugs/18046/focus=18052

Since gnulib ports the error.c file to many other platforms, but wants to keep
it in sync with glibc's version, it would be nice for glibc to apply this patch
for portability.  The attached patch makes the optimization of not calling fcntl
on glibc, while still fixing the crash from the original gnulib report.