refactor: rename GNUmakefile -> Makefile and split PHONY targets

Author: ndhoule

GNUmakefile renamed to Makefile

@@ -1,19 +1,23 @@
-.PHONY: all build deps generate help test openapi_generate
-SWAGGER_SPEC=swagger.yml
+SWAGGER_SPEC := swagger.yml
 
 help: ## Show this help.
 		@awk 'BEGIN {FS = ":.*?## "} /^[a-zA-Z_-]+:.*?## / {sub("\\\\n",sprintf("\n%22c"," "), $$2);printf "\033[36m%-20s\033[0m %s\n", $$1, $$2}' $(MAKEFILE_LIST)
+.PHONY: help
 
 all: deps openapi_generate generate test testacc # build
+.PHONY: all
 
 build: ## Build Terraform provider.
 	go install .
+.PHONY: build
 
 deps: ## Install dependencies.
 	go mod download
+.PHONY: deps
 
 generate: ## Generate Terraform docs.
 	go generate
+.PHONY: generate
 
 openapi_generate: ## Generate the go code from the OpenAPI spec.
 	docker run --rm \
@@ -26,10 +30,13 @@ openapi_generate: ## Generate the go code from the OpenAPI spec.
 	sed -i '' 's/int32/int64/g' internal/netlifyapi/model_*.go ; \
 	sed -i '' 's/int32/int64/g' internal/netlifyapi/api_*.go ; \
 	sed -i '' 's/return e.error/return fmt.Sprintf("%s: %s", e.error, e.body)/g' internal/netlifyapi/client.go
+.PHONY: openapi_generate
 
 test: ## Test the go code.
 	go test -v ./...
+.PHONY: test
 
 testacc: ## Test the go code and run acceptance tests.
 	TF_ACC=1 go test ./... -v $(TESTARGS)
 # -timeout 120m
+.PHONY: testacc