Makefile: set GOTOOLCHAIN=local

Set GOTOOLCHAIN=local for all make targets, and for renovate.

Have the "vendor" target (and by extension, "vendor-in-container", which
our validation in CI uses) clear any "toolchain" directive that might
have been added to go.mod through manual invocations of the compiler.

At this point, we probably don't need to be checking for Go module
support, so switch to assuming it's available.

Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>

.github/renovate.json5

@@ -56,4 +56,7 @@
     "**/tests/**"
   ],
 
+  "env": {
+    "GOTOOLCHAIN": "local"
+  }
 }

Makefile

@@ -1,4 +1,5 @@
 export GOPROXY=https://proxy.golang.org
+export GOTOOLCHAIN=local
 
 APPARMORTAG := $(shell hack/apparmor_tag.sh)
 STORAGETAGS := exclude_graphdriver_devicemapper $(shell ./btrfs_tag.sh) $(shell ./btrfs_installed_tag.sh) $(shell ./hack/libsubid_tag.sh)
@@ -22,14 +23,8 @@ STRIP ?= strip
 GO := go
 GO_LDFLAGS := $(shell if $(GO) version|grep -q gccgo; then echo "-gccgoflags"; else echo "-ldflags"; fi)
 GO_GCFLAGS := $(shell if $(GO) version|grep -q gccgo; then echo "-gccgoflags"; else echo "-gcflags"; fi)
-# test for go module support
-ifeq ($(shell $(GO) help mod >/dev/null 2>&1 && echo true), true)
-export GO_BUILD=GO111MODULE=on $(GO) build -mod=vendor
-export GO_TEST=GO111MODULE=on $(GO) test -mod=vendor
-else
 export GO_BUILD=$(GO) build
 export GO_TEST=$(GO) test
-endif
 RACEFLAGS := $(shell $(GO_TEST) -race ./pkg/dummy > /dev/null 2>&1 && echo -race)
 
 COMMIT_NO ?= $(shell git rev-parse HEAD 2> /dev/null || true)
@@ -209,9 +204,10 @@ vendor-in-container:
 
 .PHONY: vendor
 vendor:
-	GO111MODULE=on $(GO) mod tidy
-	GO111MODULE=on $(GO) mod vendor
-	GO111MODULE=on $(GO) mod verify
+	$(GO) mod tidy
+	$(GO) mod vendor
+	$(GO) mod verify
+	if test -n "$(strip $(shell go env GOTOOLCHAIN))"; then go mod edit -toolchain none ; fi
 
 .PHONY: lint
 lint: install.tools