gnu: Add libretro-flycast.

* gnu/packages/emulators.scm
(flycast) [source]: Preserve "libzip" bundled copy.
(libretro-flycast): New variable.

Change-Id: Ie5f1ff3e51a7fb9021a8c272d529478c9c6f3d8e

gnu/packages/emulators.scm

@@ -4380,7 +4380,8 @@ on a Commodore C64, C128 etc.")
                       ;;   (("add_subdirectory\\(core/deps/Vulkan-Headers\\)")
                       ;;    "find_package(VulkanHeaders)"))
                       (with-directory-excursion "core/deps"
-                        (for-each delete-file-recursively
+                        (for-each
+                         delete-file-recursively
                          '("SDL"
                            "Spout"
                            "Syphon"
@@ -4389,7 +4390,10 @@ on a Commodore C64, C128 etc.")
                            ;;"Vulkan-Headers"
                            "breakpad"
                            "discord-rpc"
-                                    "libzip"
+                           ;; XXX: The libretro build requires the bundled
+                           ;; libzip, which it uses to produce a
+                           ;; static library.
+                           ;;"libzip"
                            "oboe")))))))
       (build-system cmake-build-system)
       (arguments
@@ -4432,6 +4436,13 @@ on a Commodore C64, C128 etc.")
 and Atomiswave emulator derived from reicast.")
       (license license:gpl2+))))
 
+(define-public libretro-flycast
+  (package/inherit flycast
+    (name "libretro-flycast")
+    (arguments (substitute-keyword-arguments (package-arguments flycast)
+                 ((#:configure-flags flags)
+                  #~(cons "-DLIBRETRO=ON" #$flags))))))
+
 (define-public freedisksysrom
   ;; There is no release; use the latest commit.
   (let ((commit "0d5f95f109bb3aadf2bb9510bfda13879bbd5266")