add golang.org/x/sys/cpu as dependency to makefile

Makefile

@@ -4,7 +4,9 @@ PRJ_DIR      = $(abspath $(dir $(MK_FILE_PATH)))
 GOPATH_LOCAL = $(PRJ_DIR)/build
 GOPATH_DIR   = github.com/cloudflare/p751sidh
 CSHAKE_PKG   = github.com/henrydcase/nobs/hash/sha3
+CPU_PKG      = golang.org/x/sys/cpu
 TARGETS      = p751toolbox sidh sike
+GO           ?= go
 GOARCH       ?=
 OPTS_GCCGO   ?= -compiler gccgo -O2 -g
 OPTS_TAGS    ?= -tags=noasm
@@ -20,7 +22,7 @@ clean:
 	rm -rf coverage*.txt
 
 prep:
-	GOPATH=$(GOPATH_LOCAL) go get $(CSHAKE_PKG)
+	GOPATH=$(GOPATH_LOCAL) $(GO) get $(CSHAKE_PKG) $(CPU_PKG)
 	mkdir -p $(GOPATH_LOCAL)/src/$(GOPATH_DIR)
 	cp -rf p751toolbox $(GOPATH_LOCAL)/src/$(GOPATH_DIR)
 	cp -rf sidh $(GOPATH_LOCAL)/src/$(GOPATH_DIR)
@@ -28,17 +30,17 @@ prep:
 	cp -rf etc $(GOPATH_LOCAL)/src/$(GOPATH_DIR)
 
 test-%: prep
-	GOPATH=$(GOPATH_LOCAL) go test -v $(OPTS) $(GOPATH_DIR)/$*
+	GOPATH=$(GOPATH_LOCAL) $(GO) test -v $(OPTS) $(GOPATH_DIR)/$*
 
 bench-%: prep
-	cd $*; GOPATH=$(GOPATH_LOCAL) go test -v $(OPTS) -bench=.
+	cd $*; GOPATH=$(GOPATH_LOCAL) $(GO) test -v $(OPTS) -bench=.
 
 cover-%: prep
-	GOPATH=$(GOPATH_LOCAL) go test \
+	GOPATH=$(GOPATH_LOCAL) $(GO) test \
 		-race -coverprofile=coverage_$*.txt -covermode=atomic $(OPTS) $(GOPATH_DIR)/$*
 	cat coverage_$*.txt >> coverage.txt
 	rm coverage_$*.txt
 
 test: $(addprefix test-, $(TARGETS))
 bench: $(addprefix bench-, $(TARGETS))
-cover: $(addprefix cover-, $(TARGETS))
+cover: $(addprefix cover-, $(TARGETS))