feat(bazel): auto install on mac with brew

bazel.make

@@ -1,8 +1,18 @@
 BAZEL_BUILD=bazel $(BAZEL_ARGS) build $(BAZEL_CMD_ARGS)
 
+ifeq ($(UNAME_S),Darwin)
+BAZEL = /usr/local/bin/bazel
+
+$(BAZEL):
+	brew tap bazelbuild/tap
+	brew install bazelbuild/tap/bazel
+endif
+
+BAZEL ?= $(shell which bazel 2>/dev/null || echo bazel)
+
 .PHONY: bazel.banner
-bazel.banner:
-	bazel $(BAZEL_ARGS) run $(BAZEL_CMD_ARGS) //go/cmd/bertychat banner
+bazel.banner: $(BAZEL)
+	$(BAZEL) $(BAZEL_ARGS) run $(BAZEL_CMD_ARGS) //go/cmd/bertychat banner
 
 .PHONY: bazel.build
 bazel.build:
@@ -14,12 +24,12 @@ bazel.test:
 	bazel $(BAZEL_ARGS) test $(BAZEL_CMD_ARGS) //api/... //go/...
 
 .PHONY: bazel.clean
-bazel.clean:
-	bazel clean
+bazel.clean: $(BAZEL)
+	$(BAZEL) clean
 
 .PHONY: bazel.expunge
-bazel.expunge:
-	bazel clean --expunge
+bazel.expunge: $(BAZEL)
+	$(BAZEL) clean --expunge
 
 .PHONY: bazel.re
 bazel.re: bazel.expunge