quiet_system: Dump to /dev/null instead of closing

Some programs fail where they would otherwise succeed if stdout or stderr is
closed. For example, using mpicc from the mpich2 formula:

    quiet_system 'mpicc', '--version'

Fails with:

    LLVM ERROR: IO failure on output stream.

While

    system 'mpicc', '--version'

Succeeds.

Closes Homebrew/homebrew#13253.

Signed-off-by: Charlie Sharpsteen <source@sharpsteen.net>

Library/Homebrew/utils.rb

@@ -109,8 +109,10 @@ end
 # prints no output
 def quiet_system cmd, *args
   Homebrew.system(cmd, *args) do
-    $stdout.close
+    # Redirect output streams to `/dev/null` instead of closing as some programs
-    $stderr.close
+    # will fail to execute if they can't write to an open stream.
+    $stdout.reopen('/dev/null')
+    $stderr.reopen('/dev/null')
   end
 end