coqPackages.metaFetch: fix sort predicate stability

Incorrect sorting predicate was found as part of
NixOS/nix#12106 where `nix` was crashing on
the code like:

    $ nix eval --expr 'builtins.sort (a: b: true) [ 1 2 3 ]'
    ...
    Aborted (core dumped)

Note: the crash happens here because sorting predicate does not
implement `lessThan` and triggers assertion failures for
`std::stable_sort` that backs `builtins.sort`.

The change restores `lessThan` semantic for `version sorting`.

pkgs/build-support/coq/meta-fetch/default.nix

@@ -27,7 +27,7 @@ let
     sort
     switch
     switch-if
-    versionAtLeast
+    versionOlder
     versions
     ;
 
@@ -112,7 +112,7 @@ let
   shortVersion =
     x:
     if (isString x && match "^/.*" x == null) then
-      findFirst (v: versions.majorMinor v == x) null (sort versionAtLeast (attrNames release))
+      findFirst (v: versions.majorMinor v == x) null (sort (l: r: versionOlder r l) (attrNames release))
     else
       null;
   isShortVersion = x: shortVersion x != null;