buildGoPackage: Allow excluding of specific modules

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

@@ -71,13 +71,15 @@ go.stdenv.mkDerivation (
     else
         (cd go/src
         find $goPackagePath -type f -name \*.go -exec dirname {} \; | sort | uniq | while read d; do
-            local OUT;
+            [ -n "$excludedPackages" ] && echo "$d" | grep -q "$excludedPackages" && continue
+            local OUT
             if ! OUT="$(go install $buildFlags "''${buildFlagsArray[@]}" -p $NIX_BUILD_CORES -v $d 2>&1)"; then
                 if ! echo "$OUT" | grep -q 'no buildable Go source files'; then
                     echo "$OUT" >&2
                     exit 1
                 fi
             fi
+            echo "$OUT" >&2
         done)
     fi