Cross compile Skaffold, with CGO=1, using xgo

Fixes #1936

Signed-off-by: David Gageot <david@gageot.net>

Makefile

@@ -47,15 +47,19 @@ GO_LDFLAGS += -X $(VERSION_PACKAGE).gitTreeState=$(if $(shell git status --porce
 GO_LDFLAGS +="
 
 GO_FILES := $(shell find . -type f -name '*.go' -not -path "./vendor/*")
-GO_BUILD_TAGS := "kqueue"
 
 DOCSY_COMMIT:=a7141a2eac26cb598b707cab87d224f9105c315d
 
 $(BUILD_DIR)/$(PROJECT): $(BUILD_DIR)/$(PROJECT)-$(GOOS)-$(GOARCH)
 	cp $(BUILD_DIR)/$(PROJECT)-$(GOOS)-$(GOARCH) $@
 
-$(BUILD_DIR)/$(PROJECT)-%-$(GOARCH): $(GO_FILES) $(BUILD_DIR)
-	GOOS=$* GOARCH=$(GOARCH) CGO_ENABLED=0 go build -ldflags $(GO_LDFLAGS) -gcflags $(GO_GCFLAGS) -asmflags $(GO_ASMFLAGS) -tags $(GO_BUILD_TAGS) -o $@ $(BUILD_PACKAGE)
+.PHONY: xgo
+xgo:
+	go get github.com/karalabe/xgo
+
+$(BUILD_DIR)/$(PROJECT)-%-$(GOARCH): xgo $(GO_FILES) $(BUILD_DIR)
+	xgo -go 1.12 -dest $(BUILD_DIR) -out $(PROJECT) --pkg cmd/skaffold --targets=$*/$(GOARCH) -ldflags $(GO_LDFLAGS) .
+	mv $(BUILD_DIR)/$(PROJECT)-$** $@
 
 %.sha256: %
 	shasum -a 256 $< > $@
@@ -81,7 +85,7 @@ test: $(BUILD_DIR)
 
 .PHONY: install
 install: $(GO_FILES) $(BUILD_DIR)
-	GOOS=$(GOOS) GOARCH=$(GOARCH) CGO_ENABLED=0 go install -ldflags $(GO_LDFLAGS) -gcflags $(GO_GCFLAGS) -asmflags $(GO_ASMFLAGS) -tags $(GO_BUILD_TAGS) $(BUILD_PACKAGE)
+	GOOS=$(GOOS) GOARCH=$(GOARCH) CGO_ENABLED=0 go install -ldflags $(GO_LDFLAGS) -gcflags $(GO_GCFLAGS) -asmflags $(GO_ASMFLAGS) $(BUILD_PACKAGE)
 
 .PHONY: integration
 integration: install