feat(cli): add basis for new "emacs-builder" CLI tool written in Go

This will eventually replace the build-emacs-for-macos script that's
written in Ruby. The migration of functionality will happen bit by bit
over time.

Makefile

@@ -1,3 +1,166 @@
+SOURCES := $(shell \
+	find * \
+	-not -path 'sources/*' \
+	-not -path 'builds/*' \( \
+		-name "*.go" -or \
+		-name "go.mod" -or \
+		-name "go.sum" -or \
+		-name "Makefile" -or \
+		-type f -path 'internal/*' -or \
+		-type f -path 'cmd/*' -or \
+		-type f -path 'pkg/*' \
+	\) | grep -v '.DS_Store' \
+)
+
+#
+# Environment
+#
+
+# Verbose output
+ifdef VERBOSE
+V = -v
+endif
+
+BINDIR := bin
+TOOLDIR := $(BINDIR)/tools
+
+# Global environment variables for all targets
+SHELL ?= /bin/bash
+SHELL := env \
+	GO111MODULE=on \
+	GOBIN=$(CURDIR)/$(BINDIR) \
+	CGO_ENABLED=0 \
+	PATH='$(CURDIR)/$(BINDIR):$(CURDIR)/$(TOOLDIR):$(PATH)' \
+	$(SHELL)
+
+#
+# Defaults
+#
+
+# Default target
+.DEFAULT_GOAL := build
+
+#
+# Tools
+#
+
+# external tool
+define tool # 1: binary-name, 2: go-import-path
+TOOLS += $(TOOLDIR)/$(1)
+
+$(TOOLDIR)/$(1): Makefile
+	GOBIN="$(CURDIR)/$(TOOLDIR)" go install "$(2)"
+endef
+
+$(eval $(call tool,gofumpt,mvdan.cc/gofumpt@latest))
+$(eval $(call tool,golangci-lint,github.com/golangci/golangci-lint/cmd/golangci-lint@v1.40))
+$(eval $(call tool,gomod,github.com/Helcaraxan/gomod@latest))
+
+.PHONY: tools
+tools: $(TOOLS)
+
+#
+# Build
+#
+
+LDFLAGS := -w -s
+
+VERSION ?= $(shell git describe --tags --exact 2>/dev/null)
+COMMIT  ?= $(shell git rev-parse HEAD 2>/dev/null)
+DATE    ?= $(shell date '+%FT%T%z')
+
+ifeq ($(VERSION),)
+	VERSION = 0.0.0-dev
+endif
+
+CMDDIR := cmd
+BINS := $(shell test -d "$(CMDDIR)" && cd "$(CMDDIR)" && \
+	find * -maxdepth 0 -type d -exec echo $(BINDIR)/{} \;)
+
+.PHONY: build
+build: $(BINS)
+
+$(BINS): $(BINDIR)/%: $(SOURCES)
+	mkdir -p "$(BINDIR)"
+	cd "$(CMDDIR)/$*" && go build -a $(V) \
+		-o "$(CURDIR)/$(BINDIR)/$*" \
+		-ldflags "$(LDFLAGS) \
+			-X main.version=$(VERSION) \
+			-X main.commit=$(COMMIT) \
+			-X main.date=$(DATE)"
+
+#
+# Development
+#
+
+TEST ?= $$(go list ./... | grep -v 'sources/')
+
+.PHONY: clean
+clean:
+	rm -rf $(BINARY) $(TOOLS)
+	rm -f ./go.mod.tidy-check ./go.sum.tidy-check
+
+.PHONY: test
+test:
+	CGO_ENABLED=1 go test $(V) -count=1 -race $(TESTARGS) $(TEST)
+
+.PHONY: lint
+lint: $(TOOLDIR)/golangci-lint
+	golangci-lint $(V) run
+
+.PHONY: format
+format: $(TOOLDIR)/gofumpt
+	gofumpt -w .
+
+#
+# Dependencies
+#
+
+.PHONY: deps
+deps:
+	$(info Downloading dependencies)
+	go mod download
+
+.PHONY: deps-update
+deps-update:
+	$(info Downloading dependencies)
+	go get -u -t ./...
+
+.PHONY: deps-analyze
+deps-analyze: $(TOOLDIR)/gomod
+	gomod analyze
+
+.PHONY: tidy
+tidy:
+	go mod tidy $(V)
+
+.PHONY: verify
+verify:
+	go mod verify
+
+.SILENT: check-tidy
+.PHONY: check-tidy
+check-tidy:
+	cp go.mod go.mod.tidy-check
+	cp go.sum go.sum.tidy-check
+	go mod tidy
+	( \
+		diff go.mod go.mod.tidy-check && \
+		diff go.sum go.sum.tidy-check && \
+		rm -f go.mod go.sum && \
+		mv go.mod.tidy-check go.mod && \
+		mv go.sum.tidy-check go.sum \
+	) || ( \
+		rm -f go.mod go.sum && \
+		mv go.mod.tidy-check go.mod && \
+		mv go.sum.tidy-check go.sum; \
+		exit 1 \
+	)
+
+#
+# Release
+#
+
 .PHONY: new-version
 new-version: check-npx
 	npx standard-version