message: build: fix typo in previously ignored -stdlib=libc++.
  This only affects builds with --define force_libcpp=enabled.
diff: @@ -80,7 +80,7 @@ def envoy_copts(repository, test = False):
  def envoy_static_link_libstdcpp_linkopts():
  return envoy_select_force_libcpp(
  - ["--stdlib=libc++"],
  + ["-stdlib=libc++"],
  ["-static-libstdc++", "-static-libgcc"],
  )
  