use NixOS 19.03 multiarch gdb instead of custom build

.cargo/config

@@ -1,5 +1,5 @@
 [target.thumbv7em-none-eabihf]
-runner = "arm-none-eabihf-gdb -q -x openocd.gdb"
+runner = "gdb -q -x openocd.gdb"
 rustflags = [
   "-C", "link-arg=-Tlink.x",
 ]

nix/gdb.nix

@@ -1,13 +0,0 @@
-# TODO: gdb 8.2.1 from NixOS >= 19.XX is multiarch by default.
-# remove the following as `gdb` is already in scope
-
-{ stdenv, gdb }:
-
-gdb.override {
-  stdenv = stdenv.override {
-    targetPlatform = {
-      config = "arm-none-eabihf";
-      libc = "newlib";
-    };
-  };
-}

release.nix

@@ -5,7 +5,6 @@
 
 with pkgs;
 let
-  gdb = callPackage ./nix/gdb.nix {};
   adc2tcp = callPackage ./default.nix {
     inherit rustManifest;
     mozillaOverlay = import <mozillaOverlay>;
@@ -13,5 +12,4 @@ let
 in
 {
   build = lib.hydraJob adc2tcp;
-  gdb = lib.hydraJob gdb;
 }

shell.nix

@@ -3,23 +3,16 @@
 let
   mozillaOverlay = import (builtins.fetchTarball https://github.com/mozilla/nixpkgs-mozilla/archive/master.tar.gz);
   pkgs = import <nixpkgs> { overlays = [ mozillaOverlay ]; };
-  # `lib.systems.examples.armhf-embedded` from nixpkgs master
-  # (TODO: use directly starting with NixOS 19.0X)
-  targetPlatform = {
-    config = "arm-none-eabihf";
-    libc = "newlib";
-  };
 in
 with pkgs;
 let
   rustPlatform = callPackage ./nix/rustPlatform.nix {};
   openocd = callPackage ./nix/openocd.nix {};
-  gdb = callPackage ./nix/gdb.nix {};
 in
 stdenv.mkDerivation {
   name = "adc2tcp-env";
   buildInputs = with rustPlatform.rust; [
-    rustc cargo gdb
+    rustc cargo pkgs.gdb
   ];
 
   # Set Environment Variables