Pass profile dirs as args instead of profiles.el

Writing profiles.el was borderline unreadable.
`doom-profiles-autodetect` was effectively just reading in the entire
file: accepting the paths we want in the profile as individual args and
putting them together on the Emacs side is easy enough.

Accidentally fixes a bug: `user-emacs-directory` should end in a
directory separator. We now get the right value for free by using the
path we're running Doom CLI out of.

cli2.el

@@ -12,9 +12,15 @@ it. Just skip it entirely."
   :override #'doom-initialize-core-packages
   t)
 
-(defcli! build-profile-loader-for-nix-build ()
+(defcli! build-profile-loader-for-nix-build
+  ((profile-name ("-n" form) "Profile name.")
+   (profile-directory ("-p" dir) "Profile data directory.")
+   (profile-doom-dir ("-d" dir) "DOOMDIR"))
   "Write Doom's profile loader."
-  (let ((new-profiles (doom-profiles-autodetect)))
+  (let ((new-profiles `((,profile-name
+                         (user-emacs-directory . ,doom-emacs-dir)
+                         (doom-profile-data-dir . ,profile-directory)
+                         ("DOOMDIR" . ,profile-doom-dir)))))
     (doom-profiles-save new-profiles)))
 
 (defcli! build-profile-for-nix-build ()

doom.nix

@@ -257,22 +257,14 @@ let
       # Required to avoid Doom erroring out at startup.
       nativeBuildInputs = [ git ];
     } ''
-    mkdir $out
-
-    echo '
-    ((${profileName} (user-emacs-directory . "${doomSource}")
-        (doom-profile-data-dir . "'$out'/profile")
-        ("DOOMDIR" . "${finalDoomDir}")))
-    ' > profiles.el
-
-    mkdir $out/loader
+    mkdir $out $out/loader $out/profile
     export DOOMPROFILELOADFILE=$out/loader/init.el
-    export DOOMPROFILELOADPATH=$PWD/profiles.el
     export DOOMLOCALDIR=$(mktemp -d)
     # Prevent error on Emacs shutdown writing empty build cache.
     mkdir $DOOMLOCALDIR/straight
 
-    ${runtimeShell} ${doomSource}/bin/doom build-profile-loader-for-nix-build
+    ${runtimeShell} ${doomSource}/bin/doom build-profile-loader-for-nix-build \
+      -n "${profileName}" -p "$out/profile" -d "${finalDoomDir}"
 
     # With DOOMPROFILE set, doom-state-dir and friends are HOME-relative.
     export HOME=$(mktemp -d)