Re-add BINNAME and describe available vars

Author: tashian

Makefile

@@ -1,4 +1,11 @@
-# Set V=1 for verbose output.
+# Variables:
+# V=1 for verbose output.
+# BINNAME=step to change the name of the executable
+# PREFIX=bin/ to change the build output path
+# INSTALL_PREFIX=/usr/local/bin to change the install path
+# GOOS_OVERRIDE="GOOS=linux GOARCH=arm64" to change OS and arch
+# CGO_OVERRIDE="CGO_ENABLED=1" to enable CGO
+#
 # Run `make bootstrap` to set up your local environment.
 # To build using go, use `make build`
 # For a binary that's in parity with how our CI system builds,
@@ -53,6 +60,7 @@ SRC=$(shell find . -type f -name '*.go')
 GOOS_OVERRIDE ?=
 CGO_OVERRIDE ?= CGO_ENABLED=0
 OUTPUT_ROOT=output/
+BINNAME?=step
 
 GORELEASER_BUILD_ID?=default
 ifdef DEBUG
@@ -78,14 +86,14 @@ bootstra%:
 # Build
 #########################################
 
-build: $(PREFIX)bin/step
+build: $(PREFIX)bin/$(BINNAME)
 	@echo "Build Complete!"
 
-$(PREFIX)bin/step:
+$(PREFIX)bin/$(BINNAME):
 	$Q mkdir -p $(@D)
 	$Q $(GOOS_OVERRIDE) $(CGO_OVERRIDE) go build \
 		-v \
-	   	-o $(PREFIX)bin/step \
+	   	-o $(PREFIX)bin/$(BINNAME) \
 		$(GCFLAGS) $(LDFLAGS) \
 	   	github.com/smallstep/cli/cmd/step
 
@@ -96,9 +104,9 @@ goreleaser:
 	   	--snapshot \
 		--single-target \
 	   	--clean \
-		--output $(PREFIX)bin/step
+		--output $(PREFIX)bin/$(BINNAME)
 
-.PHONY: build gobuild
+.PHONY: build goreleaser
 
 
 #########################################
@@ -115,7 +123,7 @@ race:
 
 integrate: integration
 
-integration: bin/step
+integration: bin/$(BINNAME)
 	$Q $(CGO_OVERRIDE) gotestsum -- -tags=integration ./integration/...
 
 .PHONY: integrate integration
@@ -174,7 +182,7 @@ define BUNDLE_MAKE
 	# $(2) -- Go Architecture (e.g. amd64, arm, arm64, etc.)
 	# $(3) -- Go ARM architectural family (e.g. 7, 8, etc.)
 	# $(4) -- Parent directory for executables generated by 'make'.
-	$(q) GOOS=$(1) GOARCH=$(2) GOARM=$(3) PREFIX=$(4) make $(4)bin/step
+	$Q GOOS=$(1) GOARCH=$(2) GOARM=$(3) PREFIX=$(4) make $(4)bin/step
 endef
 
 binary-linux-amd64: