nrg2iso: compile on Darwin

nrg2iso's build scripts are hard-coded to use GCC. This prevents nrg2iso
from working on Darwin/macOS.

Teach nrg2iso's build scripts to use whatever compiler is installed, not
GCC specifically. This allows nrg2iso to build using Clang on macOS.

pkgs/tools/cd-dvd/nrg2iso/c-compiler.patch

···
+Support building with compilers such as Clang.
+
+--- a/Makefile
++++ b/Makefile
+@@ -1,5 +1,5 @@
+ all: nrg2iso.c
+-	gcc nrg2iso.c -o nrg2iso
++	cc nrg2iso.c -o nrg2iso
+
+ clean:
+ 	rm -f nrg2iso

pkgs/tools/cd-dvd/nrg2iso/default.nix

···
     sha256 = "sha256-O+NqQWdY/BkQRztJqNrfKiqj1R8ZdhlzNrwXS8HjBuU=";
   };
 
+  patches = [ ./c-compiler.patch ];
+
   installPhase = ''
     mkdir -pv $out/bin/
     cp -v nrg2iso $out/bin/nrg2iso
···
     description = "A linux utils for converting CD (or DVD) image generated by Nero Burning Rom to ISO format";
     homepage = "http://gregory.kokanosky.free.fr/v4/linux/nrg2iso.en.html";
     license = licenses.gpl2;
-    platforms = platforms.linux;
+    platforms = platforms.all;
   };
 }