allow customising 'go' executable with GOEXE var (#2841)

* allow customizing 'go' executable with GOEXE var

Signed-off-by: Dmitry S <dsavints@gmail.com>
---------

Signed-off-by: Dmitry S <dsavints@gmail.com>
Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>
Co-authored-by: Vincent Batts <vbatts@hashbangbash.com>

Makefile

@@ -18,11 +18,14 @@ else
 SHELL = bash -x
 endif
 
+# allow overwriting the default `go` value with the custom path to the go executable
+GOEXE ?= go
+
 # Get the currently used golang install path (in GOPATH/bin, unless GOBIN is set)
-ifeq (,$(shell go env GOBIN))
-GOBIN=$(shell go env GOPATH)/bin
+ifeq (,$(shell $(GOEXE) env GOBIN))
+GOBIN=$(shell $(GOEXE) env GOPATH)/bin
 else
-GOBIN=$(shell go env GOBIN)
+GOBIN=$(shell $(GOEXE) env GOBIN)
 endif
 
 # Set version variables for LDFLAGS
@@ -76,20 +79,20 @@ log-%:
 			}'
 
 cosign: $(SRCS)
-	CGO_ENABLED=0 go build -trimpath -ldflags "$(LDFLAGS)" -o $@ ./cmd/cosign
+	CGO_ENABLED=0 $(GOEXE) build -trimpath -ldflags "$(LDFLAGS)" -o $@ ./cmd/cosign
 
 cosign-pivkey-pkcs11key: $(SRCS)
-	CGO_ENABLED=1 go build -trimpath -tags=pivkey,pkcs11key -ldflags "$(LDFLAGS)" -o cosign ./cmd/cosign
+	CGO_ENABLED=1 $(GOEXE) build -trimpath -tags=pivkey,pkcs11key -ldflags "$(LDFLAGS)" -o cosign ./cmd/cosign
 
 .PHONY: sget
 sget: ## Build sget binary
-	go build -trimpath -ldflags "$(LDFLAGS)" -o $@ ./cmd/sget
+	$(GOEXE) build -trimpath -ldflags "$(LDFLAGS)" -o $@ ./cmd/sget
 
 .PHONY: cross
 cross:
 	$(foreach GOOS, $(PLATFORMS),\
 		$(foreach GOARCH, $(ARCHITECTURES), $(shell export GOOS=$(GOOS); export GOARCH=$(GOARCH); \
-	go build -trimpath -ldflags "$(LDFLAGS)" -o cosign-$(GOOS)-$(GOARCH) ./cmd/cosign; \
+	$(GOEXE) build -trimpath -ldflags "$(LDFLAGS)" -o cosign-$(GOOS)-$(GOARCH) ./cmd/cosign; \
 	shasum -a 256 cosign-$(GOOS)-$(GOARCH) > cosign-$(GOOS)-$(GOARCH).sha256 ))) \
 
 #####################
@@ -99,13 +102,13 @@ cross:
 golangci-lint:
 	rm -f $(GOLANGCI_LINT_BIN) || :
 	set -e ;\
-	GOBIN=$(GOLANGCI_LINT_DIR) go install github.com/golangci/golangci-lint/cmd/golangci-lint@v1.50.1 ;\
+	GOBIN=$(GOLANGCI_LINT_DIR) $(GOEXE) install github.com/golangci/golangci-lint/cmd/golangci-lint@v1.50.1 ;\
 
 lint: golangci-lint ## Run golangci-lint linter
 	$(GOLANGCI_LINT_BIN) run -n
 
 test:
-	go test $(shell go list ./... | grep -v third_party/)
+	$(GOEXE) test $(shell $(GOEXE) list ./... | grep -v third_party/)
 
 clean:
 	rm -rf cosign
@@ -178,4 +181,4 @@ include test/ci.mk
 
 .PHONY: docgen
 docgen:
-	go run -tags pivkey,pkcs11key,cgo ./cmd/help/
+	$(GOEXE) run -tags pivkey,pkcs11key,cgo ./cmd/help/