build: only build one of roach and roachccl

roachccl depends on roach internally, so specifying them both from the
top-level Makefile is redundant.

Also introduce `libs` target for testing.

Release note: None

Makefile

@@ -471,8 +471,9 @@ LIBROACH_DIR := $(BUILD_DIR)/libroach
 PROTOC_DIR := $(GOPATH)/native/$(HOST_TRIPLE)/protobuf
 PROTOC 		 := $(PROTOC_DIR)/protoc
 
-C_LIBS_OSS = $(if $(USE_STDMALLOC),,libjemalloc) libprotobuf libsnappy librocksdb libroach
-C_LIBS_CCL = $(C_LIBS_OSS) libcryptopp libroachccl
+C_LIBS_COMMON = $(if $(USE_STDMALLOC),,libjemalloc) libprotobuf libsnappy librocksdb
+C_LIBS_OSS = $(C_LIBS_COMMON) libroach
+C_LIBS_CCL = $(C_LIBS_COMMON) libcryptopp libroachccl
 
 # Go does not permit dashes in build tags. This is undocumented. Fun!
 NATIVE_SPECIFIER_TAG := $(subst -,_,$(NATIVE_SPECIFIER))$(STDMALLOC_SUFFIX)
@@ -636,7 +637,7 @@ libroach: $(LIBROACH_DIR)/Makefile $(CPP_PROTOS_TARGET)
 	@$(MAKE) --no-print-directory -C $(LIBROACH_DIR) roach
 
 .PHONY: libroachccl
-libroachccl: $(LIBROACH_DIR)/Makefile $(CPP_PROTOS_CCL_TARGET) libroach
+libroachccl: $(LIBROACH_DIR)/Makefile $(CPP_PROTOS_CCL_TARGET)
 	@$(MAKE) --no-print-directory -C $(LIBROACH_DIR) roachccl
 
 PHONY: check-libroach
@@ -677,6 +678,9 @@ CPP_PROTOS_CCL_TARGET := $(LOCAL_BIN)/.cpp_ccl_protobuf_sources
 .DEFAULT_GOAL := all
 all: $(COCKROACH)
 
+.PHONY: c-deps
+c-deps: $(C_LIBS_CCL)
+
 buildoss: BUILDTARGET = ./pkg/cmd/cockroach-oss
 buildoss: $(C_LIBS_OSS) $(UI_ROOT)/distoss/bindata.go
 

build/variables.mk

@@ -41,6 +41,7 @@ define VALID_VARS
   CXX_PATH
   C_DEPS_DIR
   C_LIBS_CCL
+  C_LIBS_COMMON
   C_LIBS_OSS
   DUPLFLAGS
   ENABLE_ROCKSDB_ASSERTIONS