contrib: Use xgo to use Cgo in cross-compiled release builds. (#5120)

This updates the release.sh script to use xgo for Linux, Windows,
and Darwin builds. This uses
https://github.com/techknowlogick/xgo/, which is a maintained
fork of https://github.com/karalabe/xgo.

This fixes the panics related to Badger compression which only
uses Zstd when Cgo is enabled. See #4995.

v20.03.0 and v20.03.1 were already built with this change to fix
macOS and Windows binaries. Linux builds were working fine.

Fixes #4995, DGRAPH-1139

contrib/release.sh

@@ -74,6 +74,7 @@ go get -u github.com/dgraph-io/dgo
 go get -u github.com/dgraph-io/badger
 go get -u github.com/golang/protobuf/protoc-gen-go
 go get -u github.com/gogo/protobuf/protoc-gen-gofast
+go get -u src.techknowlogick.com/xgo
 
 pushd $GOPATH/src/google.golang.org/grpc
   git checkout v1.13.0
@@ -119,66 +120,57 @@ popd
 
 # Build Windows.
 pushd $basedir/dgraph/dgraph
-  env GOOS=windows GOARCH=amd64 go get -v -d .
-  env GOOS=windows GOARCH=amd64 GO111MODULE=on go build -v -o dgraph-windows-amd64.exe -ldflags \
+  xgo -go="go-$GOVERSION" --targets=windows/amd64 -ldflags \
       "-X $release=$release_version -X $branch=$gitBranch -X $commitSHA1=$lastCommitSHA1 -X '$commitTime=$lastCommitTime'" .
   mkdir $TMP/windows
-  mv dgraph-windows-amd64.exe $TMP/windows/dgraph.exe
+  mv dgraph-windows-4.0-amd64.exe $TMP/windows/dgraph.exe
 popd
 
 pushd $basedir/badger/badger
-  env GOOS=windows GOARCH=amd64 go get -v -d .
-  env GOOS=windows GOARCH=amd64 GO111MODULE=on go build -v -o badger-windows-amd64.exe .
-  mv badger-windows-amd64.exe $TMP/windows/badger.exe
+  xgo -go="go-$GOVERSION" --targets=windows/amd64 .
+  mv badger-windows-4.0-amd64.exe $TMP/windows/badger.exe
 popd
 
 pushd $basedir/ratel
-  env GOOS=windows GOARCH=amd64 go get -v -d .
-  env GOOS=windows GOARCH=amd64 go build -v -o ratel-windows-amd64.exe -ldflags "-X $ratel_release=$release_version" .
-  mv ratel-windows-amd64.exe $TMP/windows/dgraph-ratel.exe
+  xgo -go="go-$GOVERSION" --targets=windows/amd64 -ldflags "-X $ratel_release=$release_version" .
+  mv ratel-windows-4.0-amd64.exe $TMP/windows/dgraph-ratel.exe
 popd
 
 # Build Darwin.
 pushd $basedir/dgraph/dgraph
-  env GOOS=darwin GOARCH=amd64 go get -v -d .
-  env GOOS=darwin GOARCH=amd64 GO111MODULE=on go build -v -o dgraph-darwin-amd64 -ldflags \
-      "-X $release=$release_version -X $branch=$gitBranch -X $commitSHA1=$lastCommitSHA1 -X '$commitTime=$lastCommitTime'" .
+  xgo -go="go-$GOVERSION" --targets=darwin-10.9/amd64 -ldflags \
+  "-X $release=$release_version -X $branch=$gitBranch -X $commitSHA1=$lastCommitSHA1 -X '$commitTime=$lastCommitTime'" .
   mkdir $TMP/darwin
-  mv dgraph-darwin-amd64 $TMP/darwin/dgraph
+  mv dgraph-darwin-10.9-amd64 $TMP/darwin/dgraph
 popd
 
 pushd $basedir/badger/badger
-  env GOOS=darwin GOARCH=amd64 go get -v -d .
-  env GOOS=darwin GOARCH=amd64 GO111MODULE=on go build -v -o badger-darwin-amd64 .
-  mv badger-darwin-amd64 $TMP/darwin/badger
+  xgo -go="go-$GOVERSION" --targets=darwin-10.9/amd64 .
+  mv badger-darwin-10.9-amd64 $TMP/darwin/badger
 popd
 
 pushd $basedir/ratel
-  env GOOS=darwin GOARCH=amd64 go get -v -d .
-  env GOOS=darwin GOARCH=amd64 go build -v -o ratel-darwin-amd64 -v -ldflags "-X $ratel_release=$release_version" .
-  mv ratel-darwin-amd64 $TMP/darwin/dgraph-ratel
+  xgo -go="go-$GOVERSION" --targets=darwin-10.9/amd64 -ldflags "-X $ratel_release=$release_version" .
+  mv ratel-darwin-10.9-amd64 $TMP/darwin/dgraph-ratel
 popd
 
 # Build Linux.
 pushd $basedir/dgraph/dgraph
-  env GOOS=linux GOARCH=amd64 go get -v -d .
-  env GOOS=linux GOARCH=amd64 GO111MODULE=on go build -v -o dgraph-linux-amd64 -ldflags \
+  xgo -go="go-$GOVERSION" --targets=linux/amd64 -ldflags \
       "-X $release=$release_version -X $branch=$gitBranch -X $commitSHA1=$lastCommitSHA1 -X '$commitTime=$lastCommitTime'" .
   strip -x dgraph-linux-amd64
   mkdir $TMP/linux
   mv dgraph-linux-amd64 $TMP/linux/dgraph
 popd
 
 pushd $basedir/badger/badger
-  env GOOS=linux GOARCH=amd64 go get -v -d .
-  env GOOS=linux GOARCH=amd64 GO111MODULE=on go build -v -o badger-linux-amd64 .
+  xgo -go="go-$GOVERSION" --targets=linux/amd64 .
   strip -x badger-linux-amd64
   mv badger-linux-amd64 $TMP/linux/badger
 popd
 
 pushd $basedir/ratel
-  env GOOS=linux GOARCH=amd64 go get -v -d .
-  env GOOS=linux GOARCH=amd64 go build -v -o ratel-linux-amd64 -ldflags "-X $ratel_release=$release_version" .
+  xgo -go="go-$GOVERSION" --targets=linux/amd64 -ldflags "-X $ratel_release=$release_version" .
   strip -x ratel-linux-amd64
   mv ratel-linux-amd64 $TMP/linux/dgraph-ratel
 popd