message: reference cargo issue
diff: @@ -85,6 +85,8 @@ COMMAND="$1"
  shift
  # Determine flags passed to all cargo invocations.
  +# This is a bit more annoying that one would hope due to
  +# <https://github.com/rust-lang/cargo/issues/6992>.
  case "$COMMAND" in
  *-debug)
  CARGO_INSTALL_FLAGS="--debug $CARGO_EXTRA_FLAGS"
  