emacs: support BSD mktemp in emacsclient.sh (#8351)
emacs: support BSD mktemp in emacsclient.sh (#8351)

Piping stdin to emacs alias on MacOS was breaking (--tmpdir is not
supported in BSD flavored mktemp).

Tested in MacOS 10.14 and debian:buster to confirm it still works in
linux.
monological/oh-my-zsh,monological/oh-my-zsh,monological/oh-my-zsh,monological/oh-my-zsh