This should restore "make chainlink" to previous behavior (#11886)

Previously, running "make chainlink" and similar commands used to be able to rebuild the chainlink executable.
That stopped working recently, after some dependency changes. This will allow it to rebuild without needing
to explicitly run "rm chainlink" each time you modify the source code or change branches.

GNUmakefile

@@ -42,12 +42,15 @@ godoc: ## Install and run godoc
 install-chainlink: operator-ui ## Install the chainlink binary.
 	go install $(GOFLAGS) .
 
+.PHONY: chainlink
 chainlink: ## Build the chainlink binary.
 	go build $(GOFLAGS) .
 
+.PHONY: chainlink-dev
 chainlink-dev: ## Build a dev build of chainlink binary.
 	go build -tags dev $(GOFLAGS) .
 
+.PHONY: chainlink-test
 chainlink-test: ## Build a test build of chainlink binary.
 	go build $(GOFLAGS) .