Description:
In macOS only, when stdout is redirected, envoy is unable to open log file /dev/stdout and reject config.

Repro steps:
with following config:

static_resources:

admin:
  access_log_path: "/dev/stdout"
  address:
    socket_address:
      address: 0.0.0.0
      port_value: 15001

and run envoy -c envoy.yaml > foo.log.