Switch to xgo for cross-compilation

Ref T529

Makefile

@@ -16,13 +16,22 @@ build: deps
 	cd cmd/writefreely; $(GOBUILD) -v
 
 build-linux: deps
-	cd cmd/writefreely; GOOS=linux GOARCH=amd64 $(GOBUILD) -v
+	@hash xgo > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
+		$(GOGET) -u github.com/karalabe/xgo; \
+	fi
+	xgo --targets=linux/amd64, -dest build/ $(LDFLAGS) -out writefreely ./cmd/writefreely
 
 build-windows: deps
-	cd cmd/writefreely; GOOS=windows GOARCH=amd64 $(GOBUILD) -v
+	@hash xgo > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
+		$(GOGET) -u github.com/karalabe/xgo; \
+	fi
+	xgo --targets=windows/amd64, -dest build/ $(LDFLAGS) -out writefreely ./cmd/writefreely
 
 build-darwin: deps
-	cd cmd/writefreely; GOOS=darwin GOARCH=amd64 $(GOBUILD) -v
+	@hash xgo > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
+		$(GOGET) -u github.com/karalabe/xgo; \
+	fi
+	xgo --targets=darwin/amd64, -dest build/ $(LDFLAGS) -out writefreely ./cmd/writefreely
 
 build-docker :
 	$(DOCKERCMD) build -t $(IMAGE_NAME):latest -t $(IMAGE_NAME):$(GITREV) .
@@ -50,15 +59,15 @@ release : clean ui
 	cp schema.sql build
 	cp sqlite.sql build
 	$(MAKE) build-linux
-	cp cmd/writefreely/$(BINARY_NAME) build
+	mv build/$(BINARY_NAME)-linux-amd64 build/$(BINARY_NAME)
 	cd build; tar -cvzf ../$(BINARY_NAME)_$(GITREV)_linux_amd64.tar.gz *
 	rm build/$(BINARY_NAME)
 	$(MAKE) build-darwin
-	cp cmd/writefreely/$(BINARY_NAME) build
+	mv build/$(BINARY_NAME)-darwin-10.6-amd64 build/$(BINARY_NAME)
 	cd build; tar -cvzf ../$(BINARY_NAME)_$(GITREV)_darwin_amd64.tar.gz *
 	rm build/$(BINARY_NAME)
 	$(MAKE) build-windows
-	cp cmd/writefreely/$(BINARY_NAME).exe build
+	mv build/$(BINARY_NAME)-windows-4.0-amd64.exe build/$(BINARY_NAME).exe
 	cd build; zip -r ../$(BINARY_NAME)_$(GITREV)_windows_amd64.zip ./*
 	$(MAKE) build-docker
 	$(MAKE) release-docker