dmrconfig: pull upstram fix for -fno-common toolchains

Without the change build failure on upxtream gcc-10 as:

    ld: hid-libusb.o:/build/source/util.h:38: multiple definition of
      `trace_flag'; main.o:/build/source/util.h:38: first defined here

pkgs/applications/radio/dmrconfig/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitHub
+{ lib, stdenv, fetchFromGitHub, fetchpatch
 , libusb1, systemd }:
 
 stdenv.mkDerivation rec {
@@ -12,6 +12,15 @@ stdenv.mkDerivation rec {
     sha256 = "1qwix75z749628w583fwp7m7kxbj0k3g159sxb7vgqxbadqqz1ab";
   };
 
+  patches = [
+    # Pull upstream fix for -fno-common toolchains.
+    (fetchpatch {
+      name = "fno-common.patch";
+      url = "https://github.com/OpenRTX/dmrconfig/commit/1a6901488db26262a6b69f80b0e795864e9e8d0a.patch";
+      sha256 = "03px1y95a8aspd251i1jj8ggqfjvkqby4lhn5pb7l5c1lzh6h762";
+    })
+  ];
+
   buildInputs = [
     libusb1 systemd
   ];