Issue containers#324 Adding a build target and ensure compilation on …

…macOS

- Making sure that build target can handle build tags and build on macOS
- Adding target to go fmt target

Makefile

@@ -5,12 +5,16 @@ SKOPEO_REPO = projectatomic/skopeo
 SKOPEO_BRANCH = master
 # Set SUDO=sudo to run container integration tests using sudo.
 SUDO =
-BUILDTAGS   = btrfs_noversion libdm_no_deferred_remove
+BUILDTAGS  ?= btrfs_noversion libdm_no_deferred_remove
 BUILDFLAGS := -tags "$(BUILDTAGS)"
 
 PACKAGES := $(shell go list ./... | grep -v github.com/containers/image/vendor)
+SOURCE_DIRS := $(shell echo $(PACKAGES) |  tr " " "\n" | awk -F '/' '{print $$4}')
 
-all: tools .gitvalidation test validate
+all: tools build .gitvalidation test validate
+
+build: vendor
+	go build $(BUILDFLAGS) $(PACKAGES)
 
 tools: tools.timestamp
 
@@ -28,7 +32,7 @@ clean:
 	rm -rf vendor tools.timestamp
 
 test: vendor
-	@go test $(BUILDFLAGS) -cover $(PACKAGES)
+	go test $(BUILDFLAGS) -cover $(PACKAGES)
 
 # This is not run as part of (make all), but Travis CI does run this.
 # Demonstarting a working version of skopeo (possibly with modified SKOPEO_REPO/SKOPEO_BRANCH, e.g.
@@ -47,6 +51,10 @@ test-skopeo:
 		$(SUDO) make BUILDTAGS="$(BUILDTAGS)" check && \
 		rm -rf $${skopeo_path}
 
+.PHONY: fmt
+fmt:
+	@gofmt -l -s -w $(SOURCE_DIRS)
+
 validate: lint
 	@go vet $(PACKAGES)
 	@test -z "$$(gofmt -s -l . | grep -ve '^vendor' | tee /dev/stderr)"

ostree/ostree_dest.go

@@ -1,3 +1,5 @@
+// +build !containers_image_ostree_stub
+
 package ostree
 
 import (

ostree/ostree_stub.go

@@ -0,0 +1,3 @@
+// +build containers_image_ostree_stub
+
+package ostree

ostree/ostree_transport.go

@@ -1,3 +1,5 @@
+// +build !containers_image_ostree_stub
+
 package ostree
 
 import (

ostree/ostree_transport_test.go

@@ -1,3 +1,5 @@
+// +build !containers_image_ostree_stub
+
 package ostree
 
 import (