melpa: Account for recent breaking change in Emacs 30

package--prepare-dependencies has been renamed in a recent revision of
Emacs 30.

pkgs/build-support/emacs/melpa.nix

@@ -44,7 +44,7 @@ import ./generic.nix { inherit lib stdenv emacs texinfo writeText gcc; } ({
       sha256 = "17z0wbqdd6fspbj43yq8biff6wfggk74xgnaf1xx6ynsp1i74is5";
     };
 
-    patches = [ ./package-build-dont-use-mtime.patch ];
+    patches = [ ./package-build-dont-use-mtime.patch ./package-build-lm-package-requires.patch ];
 
     dontConfigure = true;
     dontBuild = true;

pkgs/build-support/emacs/package-build-lm-package-requires.patch

@@ -0,0 +1,22 @@
+diff --git a/package-build.el b/package-build.el
+index e572045..32affb2 100644
+--- a/package-build.el
++++ b/package-build.el
+@@ -553,9 +553,11 @@ still be renamed."
+                         nil t)
+                        (match-string-no-properties 1)))
+                 "No description available.")
+-            (when-let ((require-lines (lm-header-multiline "package-requires")))
+-              (package--prepare-dependencies
+-               (package-read-from-string (mapconcat #'identity require-lines " "))))
++            (if (fboundp 'lm-package-requires)
++                (lm-package-requires)
++              (when-let ((require-lines (lm-header-multiline "package-requires")))
++                (package--prepare-dependencies
++                 (package-read-from-string (mapconcat #'identity require-lines " ")))))
+             :kind       (or type 'single)
+             :url        (lm-homepage)
+             :keywords   (lm-keywords-list)
+-- 
+2.42.0
+