gh: fix cross

"zowoq" wrote this commit:

  #225121 (comment)

pkgs/applications/version-management/gh/default.nix

@@ -1,4 +1,4 @@
-{ lib, fetchFromGitHub, buildGoModule, installShellFiles, testers, gh }:
+{ lib, fetchFromGitHub, buildGoModule, installShellFiles, stdenv, testers, gh }:
 
 buildGoModule rec {
   pname = "gh";
@@ -15,27 +15,23 @@ buildGoModule rec {
 
   nativeBuildInputs = [ installShellFiles ];
 
-  # upstream unsets these to handle cross but it breaks our build
-  postPatch = ''
-    substituteInPlace Makefile \
-      --replace "GOOS= GOARCH= GOARM= GOFLAGS= CGO_ENABLED=" ""
-  '';
-
   buildPhase = ''
     runHook preBuild
-    make GO_LDFLAGS="-s -w" GH_VERSION=${version} bin/gh manpages
+    make GO_LDFLAGS="-s -w" GH_VERSION=${version} bin/gh ${lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) "manpages"}
     runHook postBuild
   '';
 
   installPhase = ''
     runHook preInstall
     install -Dm755 bin/gh -t $out/bin
+   '' + lib.optionalString (stdenv.buildPlatform.canExecute stdenv.hostPlatform) ''
     installManPage share/man/*/*.[1-9]
 
     installShellCompletion --cmd gh \
       --bash <($out/bin/gh completion -s bash) \
       --fish <($out/bin/gh completion -s fish) \
       --zsh <($out/bin/gh completion -s zsh)
+  '' + ''
     runHook postInstall
   '';