buildGo{Module,Package}: warn if buildFlags is used

pkgs/development/go-modules/generic/default.nix

···
 # Not needed with buildGoModule
 , goPackagePath ? ""
 
+# needed for buildFlags warning
+, buildFlags ? ""
+
 , ... }@args':
 
 with builtins;
···
     };
   });
 in
+lib.warnIf (buildFlags != "")
+  "Use the `ldflags` and/or `tags` attributes instead of `buildFlags`"
   package

pkgs/development/go-packages/generic/default.nix

···
 
 , CGO_ENABLED ? go.CGO_ENABLED
 
+# needed for buildFlags warning
+, buildFlags ? ""
+
 , meta ? {}, ... } @ args:
 
 
···
     } // meta;
   });
 in
+lib.warnIf (buildFlags != "")
+  "Use the `ldflags` and/or `tags` attributes instead of `buildFlags`"
   package