Rename GOFLAGS make variable to LDFLAGS

Makefile

@@ -4,7 +4,7 @@ BINARY   := go-cache-plugin
 PKG      := github.com/tailscale/go-cache-plugin/cmd/go-cache-plugin
 DIST     := dist
 UPSTREAM := $(shell go list -m -f '{{.Version}}' github.com/tailscale/go-cache-plugin)
-GOFLAGS  := -ldflags="-s -w"
+LDFLAGS  := -s -w
 OS       ?= $(shell go env GOOS)
 ARCH     ?= $(shell go env GOARCH)
 
@@ -14,7 +14,7 @@ all: build
 
 # Static so the released binary runs on any image in the estate, Alpine included.
 build:
-	CGO_ENABLED=0 GOOS=$(OS) GOARCH=$(ARCH) go build $(GOFLAGS) -o $(DIST)/$(BINARY) $(PKG)
+	CGO_ENABLED=0 GOOS=$(OS) GOARCH=$(ARCH) go build -ldflags="$(LDFLAGS)" -o $(DIST)/$(BINARY) $(PKG)
 
 # -count=1: the tests build via `make build`, and the Makefile is not a go test
 # cache input, so a cached PASS would outlive a broken build recipe.