packer: fixes compilation issues (#18217)

* the default output for buildGoPackage is not "out" anymore
* go 1.7 has removed the linker flag deprecation which breaks packer's
  Makefile

pkgs/development/tools/packer/default.nix

@@ -5,9 +5,9 @@ stdenv.mkDerivation rec {
   name = "packer-${version}";
   version = "0.10.1";
 
-  src = import ./deps.nix {
+  src = (import ./deps.nix {
     inherit stdenv lib gox gotools buildGoPackage fetchgit fetchhg fetchbzr fetchsvn;
-  };
+  }).out;
 
   buildInputs = [ src.go gox gotools ];
 

pkgs/top-level/all-packages.nix

@@ -170,7 +170,17 @@ in
 
   fetchMavenArtifact = callPackage ../build-support/fetchmavenartifact { };
 
-  packer = callPackage ../development/tools/packer { };
+  packer = callPackage ../development/tools/packer {
+    # Go 1.7 changed the linker flag format
+    buildGoPackage = buildGo16Package;
+    gotools = self.gotools.override {
+      buildGoPackage = buildGo16Package;
+      go = self.go_1_6;
+    };
+    gox = self.gox.override {
+      buildGoPackage = buildGo16Package;
+    };
+  };
 
   fetchpatch = callPackage ../build-support/fetchpatch { };