libs/db: conditional compilation

For cleveldb: go build -tags cleveldb
For boltdb: go build -tags boltdb

Fixes #3611

Makefile

@@ -23,7 +23,7 @@ build:
 	CGO_ENABLED=0 go build $(BUILD_FLAGS) -tags $(BUILD_TAGS) -o $(OUTPUT) ./cmd/tendermint/
 
 build_c:
-	CGO_ENABLED=1 go build $(BUILD_FLAGS) -tags "$(BUILD_TAGS) gcc" -o $(OUTPUT) ./cmd/tendermint/
+	CGO_ENABLED=1 go build $(BUILD_FLAGS) -tags "$(BUILD_TAGS) cleveldb" -o $(OUTPUT) ./cmd/tendermint/
 
 build_race:
 	CGO_ENABLED=0 go build -race $(BUILD_FLAGS) -tags $(BUILD_TAGS) -o $(OUTPUT) ./cmd/tendermint
@@ -32,7 +32,7 @@ install:
 	CGO_ENABLED=0 go install  $(BUILD_FLAGS) -tags $(BUILD_TAGS) ./cmd/tendermint
 
 install_c:
-	CGO_ENABLED=1 go install  $(BUILD_FLAGS) -tags "$(BUILD_TAGS) gcc" ./cmd/tendermint
+	CGO_ENABLED=1 go install  $(BUILD_FLAGS) -tags "$(BUILD_TAGS) cleveldb" ./cmd/tendermint
 
 ########################################
 ### Protobuf
@@ -132,7 +132,7 @@ clean_certs:
 	rm -f db/remotedb/::.crt db/remotedb/::.key
 
 test_libs: gen_certs
-	go test -tags gcc $(PACKAGES)
+	go test -tags clevedb boltdb $(PACKAGES)
 	make clean_certs
 
 grpc_dbserver:

libs/db/backend_test.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+
 	cmn "github.com/tendermint/tendermint/libs/common"
 )
 

libs/db/boltdb.go

@@ -1,3 +1,4 @@
+// +build boltdb
 package db
 
 import (

libs/db/boltdb_test.go

@@ -1,3 +1,4 @@
+// +build boltdb
 package db
 
 import (

libs/db/c_level_db.go

@@ -1,5 +1,4 @@
-// +build gcc
-
+// +build cleveldb
 package db
 
 import (

libs/db/c_level_db_test.go

@@ -1,5 +1,4 @@
-// +build gcc
-
+// +build cleveldb
 package db
 
 import (