treewide: Don't use envHook anymore

This commits needs a MAJOR audit as I oftentimes just guessed which of
`$hostOffset`, `$targetOffset`, or a fixed offset should be used.

pkgs/build-support/emacs/setup-hook.sh

@@ -4,4 +4,8 @@ addEmacsVars () {
   fi
 }
 
-envHooks+=(addEmacsVars)
+# If this is for a wrapper derivation, emacs and the dependencies are all
+# run-time dependencies. If this is for precompiling packages into bytecode,
+# emacs is a compile-time dependency of the package.
+addEnvHooks "$targetOffset" addEmacsVars
+addEnvHooks "$targetOffset" addEmacsVars