bug#50748: 28.0.50; tramp-sh.el uses mknod file p which is not available on macos

[Damien Merenne]

I'm trying to use eglot over tramp using `emacs -Q -f package-initialize
-L /path/to/my/eglot -l eglot.el`. From what I understand, to
capture the remote process stderr, tramp creates a fifo, in
`tramp-sh-handle-make-process`, `tramp-sh.el:2889`. The MacOS mknod
command does not support the "p" parameter, so the communication with
the process does not work. Also no error is reported while the mknod
command is failing. I tried replacing `mknod %s p` with `mkfifo %s` or using 
gnu coreutils mknod. This
fixes the fifo creation but the process communication is still
broken after that.

I can reproduce the problem with

(let ((default-directory "/ssh:macos-laptop:"))
  (make-process
   :name "TEST"
   :buffer "*TEST*"
   :command '("sh" "-c" "while sleep 1; do echo $(hostname) out; echo 
$(hostname) err >&2; done")
   :connection-type 'pipe
   :coding 'utf-8-emacs-unix
   :noquery t
   :stderr (get-buffer-create "*TEST stderr*")
   :file-handler t))

And it works correctly with

(let ((default-directory "/ssh:localhost:"))
  (make-process
   :name "TEST"
   :buffer "*TEST*"
   :command '("sh" "-c" "while sleep 1; do echo $(hostname) out; echo 
$(hostname) err >&2; done")
   :connection-type 'pipe
   :coding 'utf-8-emacs-unix
   :noquery t
   :stderr (get-buffer-create "*TEST stderr*")
   :file-handler t))



In GNU Emacs 28.0.50 (build 5, x86_64-pc-linux-gnu, GTK+ Version 3.24.25, cairo 
version 1.16.0)
 of 2021-09-16 built on workstation.lan
Repository revision: 7f53446a10eaf029f73e637bba3c9c6bf7c33111
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101001
System Description: Ubuntu 21.04

Configured using:
 'configure --with-native-compilation --with-mailutils --with-gnutls
 --with-modules --with-json --without-gpm --with-file-notification=yes
 --with-xwidgets --without-selinux --with-libsystemd --with-jpeg
 --with-tiff --with-gif --with-png --with-rsvg --with-imagemagick
 CC=gcc-10'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ
IMAGEMAGICK JPEG JSON LCMS2 LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP
NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF
TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM XWIDGETS GTK3 ZLIB

Important settings:
  value of $LC_MONETARY: fr_BE.UTF-8
  value of $LC_NUMERIC: fr_BE.UTF-8
  value of $LC_TIME: fr_BE.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: C++//lw

Minor modes in effect:
  cov-mode: t
  bloom-global-minor-mode: t
  bloom-minor-mode: t
  eglot--managed-mode: t
  flymake-mode: t
  flyspell-mode: t
  bug-reference-prog-mode: t
  magit-wip-after-apply-mode: t
  global-git-commit-mode: t
  magit-auto-revert-mode: t
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  dtrt-indent-mode: t
  test-runner-mode: t
  pdf-occur-global-minor-mode: t
  yas-global-mode: t
  yas-minor-mode: t
  subword-mode: t
  smartparens-global-mode: t
  smartparens-mode: t
  show-paren-mode: t
  auto-revert-mode: t
  marginalia-mode: t
  selectrum-mode: t
  corfu-global-mode: t
  corfu-mode: t
  global-ligature-mode: t
  ligature-mode: t
  shell-dirtrack-mode: t
  envrc-global-mode: t
  envrc-mode: t
  bepo-global-mode: t
  which-key-mode: t
  savehist-mode: t
  global-so-long-mode: t
  override-global-mode: t
  straight-use-package-mode: t
  straight-package-neutering-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  auto-fill-function: yas--auto-fill
  transient-mark-mode: t
  abbrev-mode: t

Load-path shadows:
/home/dam/.emacs.d/straight/build/transient/transient hides 
/usr/local/share/emacs/28.0.50/lisp/transient
/home/dam/.emacs.d/straight/build/jsonrpc/jsonrpc hides 
/usr/local/share/emacs/28.0.50/lisp/jsonrpc
/home/dam/.emacs.d/straight/build/xref/xref hides 
/usr/local/share/emacs/28.0.50/lisp/progmodes/xref
/home/dam/.emacs.d/straight/build/flymake/flymake hides 
/usr/local/share/emacs/28.0.50/lisp/progmodes/flymake
/home/dam/.emacs.d/straight/build/project/project hides 
/usr/local/share/emacs/28.0.50/lisp/progmodes/project
/home/dam/.emacs.d/straight/build/let-alist/let-alist hides 
/usr/local/share/emacs/28.0.50/lisp/emacs-lisp/let-alist
/home/dam/.emacs.d/straight/build/eldoc/eldoc hides 
/usr/local/share/emacs/28.0.50/lisp/emacs-lisp/eldoc

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Memory information:
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 (symbols 48 48827 4)
 (strings 32 188566 42756)
 (string-bytes 1 7819478)
 (vectors 16 95165)
 (vector-slots 8 2534894 561288)
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