Adds :delegated flags to speed up build experience on MacOS.

This is ignored by other OS, see https://docs.docker.com/docker-for-mac/osxfs-caching/#delegated.

Signed-off-by: Cyril Tovena <cyril.tovena@gmail.com>

Makefile

@@ -67,6 +67,8 @@ DYN_GO_FLAGS := -ldflags "-s -w $(GO_LDFLAGS)" -tags netgo $(MOD_FLAG)
 # Also remove the -s and -w flags present in the normal build which strip the symbol table and the DWARF symbol table.
 DEBUG_GO_FLAGS     := -gcflags "all=-N -l" -ldflags "-extldflags \"-static\" $(GO_LDFLAGS)" -tags netgo $(MOD_FLAG)
 DYN_DEBUG_GO_FLAGS := -gcflags "all=-N -l" -ldflags "$(GO_LDFLAGS)" -tags netgo $(MOD_FLAG)
+# Docker mount flag, ignored on native docker host. see (https://docs.docker.com/docker-for-mac/osxfs-caching/#delegated)
+MOUNT_FLAGS := :delegated
 
 NETGO_CHECK = @strings $@ | grep cgo_stub\\\.go >/dev/null || { \
        rm $@; \
@@ -272,9 +274,9 @@ ifeq ($(BUILD_IN_CONTAINER),true)
 	@mkdir -p $(shell pwd)/.pkg
 	@mkdir -p $(shell pwd)/.cache
 	$(SUDO) docker run $(RM) $(TTY) -i \
-		-v $(shell pwd)/.cache:/go/cache \
-		-v $(shell pwd)/.pkg:/go/pkg \
-		-v $(shell pwd):/src/loki \
+		-v $(shell pwd)/.cache:/go/cache$(MOUNT_FLAGS) \
+		-v $(shell pwd)/.pkg:/go/pkg$(MOUNT_FLAGS) \
+		-v $(shell pwd):/src/loki$(MOUNT_FLAGS) \
 		$(IMAGE_PREFIX)/loki-build-image:$(BUILD_IMAGE_VERSION) $@;
 else
 	goyacc -p $(basename $(notdir $<)) -o $@ $<
@@ -297,9 +299,9 @@ ifeq ($(BUILD_IN_CONTAINER),true)
 	@mkdir -p $(shell pwd)/.pkg
 	@mkdir -p $(shell pwd)/.cache
 	$(SUDO) docker run $(RM) $(TTY) -i \
-		-v $(shell pwd)/.cache:/go/cache \
-		-v $(shell pwd)/.pkg:/go/pkg \
-		-v $(shell pwd):/src/loki \
+		-v $(shell pwd)/.cache:/go/cache$(MOUNT_FLAGS) \
+		-v $(shell pwd)/.pkg:/go/pkg$(MOUNT_FLAGS) \
+		-v $(shell pwd):/src/loki$(MOUNT_FLAGS) \
 		$(IMAGE_PREFIX)/loki-build-image:$(BUILD_IMAGE_VERSION) $@;
 else
 	case "$@" in	\
@@ -516,9 +518,9 @@ ifeq ($(BUILD_IN_CONTAINER),true)
 	@mkdir -p $(shell pwd)/.pkg
 	@mkdir -p $(shell pwd)/.cache
 	$(SUDO) docker run $(RM) $(TTY) -i \
-		-v $(shell pwd)/.cache:/go/cache \
-		-v $(shell pwd)/.pkg:/go/pkg \
-		-v $(shell pwd):/src/loki \
+		-v $(shell pwd)/.cache:/go/cache$(MOUNT_FLAGS) \
+		-v $(shell pwd)/.pkg:/go/pkg$(MOUNT_FLAGS) \
+		-v $(shell pwd):/src/loki$(MOUNT_FLAGS) \
 		$(IMAGE_PREFIX)/loki-build-image:$(BUILD_IMAGE_VERSION) $@;
 else
 	drone jsonnet --stream --format -V __build-image-version=$(BUILD_IMAGE_VERSION) --source .drone/drone.jsonnet --target .drone/drone.yml
@@ -529,8 +531,8 @@ endif
 check-mod:
 ifeq ($(BUILD_IN_CONTAINER),true)
 	$(SUDO) docker run  $(RM) $(TTY) -i \
-		-v $(shell go env GOPATH)/pkg:/go/pkg \
-		-v $(shell pwd):/src/loki \
+		-v $(shell go env GOPATH)/pkg:/go/pkg$(MOUNT_FLAGS) \
+		-v $(shell pwd):/src/loki$(MOUNT_FLAGS) \
 		$(IMAGE_PREFIX)/loki-build-image:$(BUILD_IMAGE_VERSION) $@;
 else
 	GO111MODULE=on GOPROXY=https://proxy.golang.org go mod download