Makefile: parse TENDERMINT_BUILD_OPTIONS

Reduce the number of targets and make the buildsystem more
flexible by parsing the TENDERMINT_BUILD_OPTIONS command
line variable (a-la Debian, inspired by dpkg-buildpackage's
DEB_BUILD_OPTIONS), e.g:

 $ make install TENDERMINT_BUILD_OPTIONS='cleveldb'

replaces the old:

 $ make install_c

Options can be mix&match'd, e.g.:

 $ make install TENDERMINT_BUILD_OPTIONS='cleveldb race nostrip'

Three options are available:
- nostrip: don't strip debugging symbols nor DWARF tables.
- cleveldb: use cleveldb as db backend instead of goleveldb;
  it switches on the CGO_ENABLED Go environment variale.
- race: pass -race to go build and enable data race detection.

This changeset is a port of gaia pull request: cosmos/gaia#363

Makefile

@@ -1,11 +1,33 @@
 PACKAGES=$(shell go list ./...)
 OUTPUT?=build/tendermint
 
-BUILD_TAGS?='tendermint'
-LD_FLAGS = -X github.com/tendermint/tendermint/version.GitCommit=`git rev-parse --short=8 HEAD` -s -w
+BUILD_TAGS?=tendermint
+LD_FLAGS = -X github.com/tendermint/tendermint/version.GitCommit=`git rev-parse --short=8 HEAD`
 BUILD_FLAGS = -mod=readonly -ldflags "$(LD_FLAGS)"
 HTTPS_GIT := https://github.com/tendermint/tendermint.git
 DOCKER_BUF := docker run -v $(shell pwd):/workspace --workdir /workspace bufbuild/buf
+CGO_ENABLED ?= 0
+
+# handle nostrip
+ifeq (,$(findstring nostrip,$(TENDERMINT_BUILD_OPTIONS)))
+  BUILD_FLAGS += -trimpath
+  LD_FLAGS += -s -w
+endif
+
+# handle race
+ifeq (race,$(findstring race,$(TENDERMINT_BUILD_OPTIONS)))
+  CGO_ENABLED=1
+  BUILD_FLAGS += -race
+endif
+
+# handle cleveldb
+ifeq (cleveldb,$(findstring cleveldb,$(TENDERMINT_BUILD_OPTIONS)))
+  CGO_ENABLED=1
+  BUILD_TAGS += cleveldb
+endif
+
+# allow users to pass additional flags via the conventional LDFLAGS variable
+LD_FLAGS += $(LDFLAGS)
 
 all: check build test install
 .PHONY: all
@@ -19,25 +41,13 @@ include tests.mk
 ###############################################################################
 
 build:
-	CGO_ENABLED=0 go build $(BUILD_FLAGS) -tags $(BUILD_TAGS) -o $(OUTPUT) ./cmd/tendermint/
+	CGO_ENABLED=$(CGO_ENABLED) go build $(BUILD_FLAGS) -tags '$(BUILD_TAGS)' -o $(OUTPUT) ./cmd/tendermint/
 .PHONY: build
 
-build_c:
-	CGO_ENABLED=1 go build $(BUILD_FLAGS) -tags "$(BUILD_TAGS) cleveldb" -o $(OUTPUT) ./cmd/tendermint/
-.PHONY: build_c
-
-build_race:
-	CGO_ENABLED=1 go build -race $(BUILD_FLAGS) -tags $(BUILD_TAGS) -o $(OUTPUT) ./cmd/tendermint
-.PHONY: build_race
-
 install:
-	CGO_ENABLED=0 go install $(BUILD_FLAGS) -tags $(BUILD_TAGS) ./cmd/tendermint
+	CGO_ENABLED=$(CGO_ENABLED) go install $(BUILD_FLAGS) -tags $(BUILD_TAGS) ./cmd/tendermint
 .PHONY: install
 
-install_c:
-	CGO_ENABLED=1 go install $(BUILD_FLAGS) -tags "$(BUILD_TAGS) cleveldb" ./cmd/tendermint
-.PHONY: install_c
-
 ###############################################################################
 ###                                Protobuf                                 ###
 ###############################################################################