lib.addMetaAttrs: use overrideAttrs when available

Previously, any subsequent change to a derivation after
an `addMetaAttrs` call would cause said attribute(s) to
be unconditionally reset back to their previous value(s):

    nix-repl> ((oldPkgs.lib.lowPrio oldPkgs.hello).overrideAttrs {a = 1;}).meta.priority
    error:
        … while evaluating the attribute 'meta.priority'
            at /nix/store/nxdiklm6dnf9pma1zg7srls2nzrykrjf-nixos/nixos/pkgs/stdenv/generic/make-derivation.nix:846:17:
            845|         inherit passthru overrideAttrs;
            846|         inherit meta;
                |                 ^
            847|       }

        error: attribute 'priority' missing
        at «string»:1:67:
                1| ((oldPkgs.lib.lowPrio oldPkgs.hello).overrideAttrs {a = 1;}).meta.priority
                |                                                                   ^

This change makes it so that this does not happen (unless, of
course, a subsequent override does affect those values):

    nix-repl> ((newPkgs.lib.lowPrio oldPkgs.hello).overrideAttrs {a = 1;}).meta.priority
    10

Fixes #323624.

lib/meta.nix

@@ -44,7 +44,14 @@ rec {
 
     :::
   */
-  addMetaAttrs = newAttrs: drv: drv // { meta = (drv.meta or { }) // newAttrs; };
+  addMetaAttrs =
+    newAttrs: drv:
+    if drv ? overrideAttrs then
+      drv.overrideAttrs (old: {
+        meta = (old.meta or { }) // newAttrs;
+      })
+    else
+      drv // { meta = (drv.meta or { }) // newAttrs; };
 
   /**
     Disable Hydra builds of given derivation.