go: Fix build when targetting MinGW

pkgs/development/compilers/go/1.17.nix

@@ -18,8 +18,12 @@
 , buildPackages
 , pkgsBuildTarget
 , callPackage
+, threadsCross ? null # for MinGW
 }:
 
+# threadsCross is just for MinGW
+assert threadsCross != null -> stdenv.targetPlatform.isWindows;
+
 let
   go_bootstrap = buildPackages.callPackage ./bootstrap.nix { };
 
@@ -50,6 +54,8 @@ let
   # We need a target compiler which is still runnable at build time,
   # to handle the cross-building case where build != host == target
   targetCC = pkgsBuildTarget.targetPackages.stdenv.cc;
+
+  isCross = stdenv.buildPlatform != stdenv.targetPlatform;
 in
 
 stdenv.mkDerivation rec {
@@ -71,6 +77,10 @@ stdenv.mkDerivation rec {
 
   depsTargetTargetPropagated = lib.optionals stdenv.isDarwin [ Security Foundation ];
 
+  depsBuildTarget = lib.optional isCross targetCC;
+
+  depsTargetTarget = lib.optional (threadsCross != null) threadsCross;
+
   hardeningDisable = [ "all" ];
 
   prePatch = ''
@@ -194,12 +204,12 @@ stdenv.mkDerivation rec {
   # {CC,CXX}_FOR_TARGET must be only set for cross compilation case as go expect those
   # to be different from CC/CXX
   CC_FOR_TARGET =
-    if (stdenv.buildPlatform != stdenv.targetPlatform) then
+    if isCross then
       "${targetCC}/bin/${targetCC.targetPrefix}cc"
     else
       null;
   CXX_FOR_TARGET =
-    if (stdenv.buildPlatform != stdenv.targetPlatform) then
+    if isCross then
       "${targetCC}/bin/${targetCC.targetPrefix}c++"
     else
       null;
@@ -223,7 +233,7 @@ stdenv.mkDerivation rec {
 
     export PATH=$(pwd)/bin:$PATH
 
-    ${lib.optionalString (stdenv.buildPlatform != stdenv.targetPlatform) ''
+    ${lib.optionalString isCross ''
     # Independent from host/target, CC should produce code for the building system.
     # We only set it when cross-compiling.
     export CC=${buildPackages.stdenv.cc}/bin/cc