fix(cli): increment __DOOMSTEP in elisp instead

Some shells (like ksh on SDF) may complain about $((...)) arithmetic
expansion syntax. Rather than wrestle with old shells, I'll offload this
trivial operation to elisp instead.

Close: #6970

bin/doom

@@ -5,7 +5,7 @@
 :; tmpdir=`$emacs --eval '(princ (temporary-file-directory))' 2>/dev/null`
 :; [ -z "$tmpdir" ] && { >&2 echo "Error: failed to run Emacs with command '$EMACS'"; >&2 echo; >&2 echo "Are you sure Emacs is installed and in your \$PATH?"; exit 1; }
 :; export __DOOMPID="${__DOOMPID:-$$}"
-:; export __DOOMSTEP="$((__DOOMSTEP+1))"
+:; export __DOOMSTEP="${__DOOMSTEP:-0}"
 :; export __DOOMGEOM="${__DOOMGEOM:-`tput cols 2>/dev/null`x`tput lines 2>/dev/null`}"
 :; export __DOOMGPIPE=${__DOOMGPIPE:-$__DOOMPIPE}
 :; export __DOOMPIPE=; [ -t 0 ] || __DOOMPIPE="${__DOOMPIPE}0"; [ -t 1 ] || __DOOMPIPE="${__DOOMPIPE}1"

bin/doomscript

@@ -57,7 +57,7 @@ fi
 # Some state that Doom's CLI framework needs to know about the terminal. Read
 # the comments at the top of bin/doom for explanations.
 export __DOOMPID="${__DOOMPID:-$$}"
-export __DOOMSTEP="$((__DOOMSTEP+1))"
+export __DOOMSTEP="${__DOOMSTEP:-0}"
 export __DOOMGEOM="${__DOOMGEOM:-$(tput cols 2>/dev/null)x$(tput lines 2>/dev/null)}"
 export __DOOMGPIPE="${__DOOMGPIPE:-$__DOOMPIPE}"
 export __DOOMPIPE=