Enforce netgo build tag while cross-compilation (#1690)

Makefile

@@ -140,7 +140,7 @@ release-windows:
 	@hash xgo > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
 		go get -u github.com/karalabe/xgo; \
 	fi
-	xgo -dest $(DIST)/binaries -tags '$(TAGS)' -ldflags '-linkmode external -extldflags "-static" $(LDFLAGS)' -targets 'windows/*' -out gitea-$(VERSION) .
+	xgo -dest $(DIST)/binaries -tags 'netgo $(TAGS)' -ldflags '-linkmode external -extldflags "-static" $(LDFLAGS)' -targets 'windows/*' -out gitea-$(VERSION) .
 ifeq ($(CI),drone)
 	mv /build/* $(DIST)/binaries
 endif
@@ -150,7 +150,7 @@ release-linux:
 	@hash xgo > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
 		go get -u github.com/karalabe/xgo; \
 	fi
-	xgo -dest $(DIST)/binaries -tags '$(TAGS)' -ldflags '-linkmode external -extldflags "-static" $(LDFLAGS)' -targets 'linux/*' -out gitea-$(VERSION) .
+	xgo -dest $(DIST)/binaries -tags 'netgo $(TAGS)' -ldflags '-linkmode external -extldflags "-static" $(LDFLAGS)' -targets 'linux/*' -out gitea-$(VERSION) .
 ifeq ($(CI),drone)
 	mv /build/* $(DIST)/binaries
 endif
@@ -160,7 +160,7 @@ release-darwin:
 	@hash xgo > /dev/null 2>&1; if [ $$? -ne 0 ]; then \
 		go get -u github.com/karalabe/xgo; \
 	fi
-	xgo -dest $(DIST)/binaries -tags '$(TAGS)' -ldflags '$(LDFLAGS)' -targets 'darwin/*' -out gitea-$(VERSION) .
+	xgo -dest $(DIST)/binaries -tags 'netgo $(TAGS)' -ldflags '$(LDFLAGS)' -targets 'darwin/*' -out gitea-$(VERSION) .
 ifeq ($(CI),drone)
 	mv /build/* $(DIST)/binaries
 endif