packages: Recognize the '.Z' extension.

Reported by thomasd on #guix.

* guix/packages.scm (patch-and-repack)[decompression-type]: Add "Z".

guix/packages.scm

@@ -406,6 +406,7 @@ (define lookup-input
 
   (define decompression-type
     (cond ((string-suffix? "gz" source-file-name)  "gzip")
+          ((string-suffix? "Z" source-file-name)  "gzip")
           ((string-suffix? "bz2" source-file-name) "bzip2")
           ((string-suffix? "lz" source-file-name)  "lzip")
           ((string-suffix? "zip" source-file-name) "unzip")