gnu: Add gens-gs.

* gnu/packages/emulators.scm (gens-gs): New variable.

gnu/packages/emulators.scm

@@ -10,6 +10,7 @@
 ;;; Copyright © 2017 Tobias Geerinckx-Rice <me@tobias.gr>
 ;;; Copyright © 2017, 2018, 2019 Rutger Helling <rhelling@mykolab.com>
 ;;; Copyright © 2019 Pierre Neidhardt <mail@ambrevar.xyz>
+;;; Copyright © 2019 David Wilson <david@daviwil.com>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -85,6 +86,7 @@ (define-module (gnu packages emulators)
   #:use-module (gnu packages xorg)
   #:use-module (gnu packages web)
   #:use-module (guix build-system cmake)
+  #:use-module (guix build-system glib-or-gtk)
   #:use-module (guix build-system gnu))
 
 (define-public desmume
@@ -1422,3 +1424,41 @@ (define-public pcsxr
        "A PlayStation emulator based on PCSX-df Project with bugfixes and
 improvements.")
       (license license:gpl2+))))
+
+(define-public gens-gs
+  (package
+    (name "gens-gs")
+    (version "7")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (string-append "https://retrocdn.net/images/6/6d/Gens-gs-r"
+                           version ".tar.gz"))
+       (sha256
+        (base32
+         "1ha5s6d3y7s9aq9f4zmn9p88109c3mrj36z2w68jhiw5xrxws833"))))
+    (build-system glib-or-gtk-build-system)
+    (arguments
+     `(#:system "i686-linux"
+       #:phases
+       (modify-phases %standard-phases
+         (add-after 'unpack 'fix-CFLAGS
+           (lambda* _
+             ;; Remove GTK API deprecation flags that cause build errors.
+             (substitute* "configure"
+               (("GTK_CFLAGS=\"\\$GTK_CFLAGS .*\"") ""))
+             #t)))))
+    (native-inputs
+     `(("pkg-config" ,pkg-config)
+       ("nasm" ,nasm)))
+    (inputs
+     `(("sdl" ,sdl)
+       ("gtk" ,gtk+-2)))
+    (home-page "https://segaretro.org/Gens/GS")
+    (synopsis "Emulator for Sega Genesis/Mega Drive systems")
+    (description
+     "Gens/GS is an emulator for the Mega Drive (also known as Sega Genesis),
+derived from Gens.  Project goals include clean source code, combined features
+from various forks of Gens, and improved platform portability.")
+    (supported-systems '("i686-linux" "x86_64-linux"))
+    (license license:gpl2+)))