cmd/buildlet{,stage0}: use go version in go.mod via go.dev/doc/toolchain

Both go1.22.8 and go1.19 are old and need to be updated to go1.23+.

As of Go 1.21, instead of doing:

	go install golang.org/dl/go1.n.m@latest
	go1.n.m download

to get a specific Go toolchain version, we can do:

	env GOTOOLCHAIN=go1.n.m go

But there's probably no good reason not to permit newer versions than
go1.n.m if the x/build go.mod go directive is upgraded to a higher Go
version, so it should be:

	env GOTOOLCHAIN=go1.n.m+auto go

But that means in most cases exactly go1.n.m will be used, even if the
local Go toolchain is slightly newer.

Instead of maintaining the Go version both here and in x/build's go.mod
file, reuse the top-level one. Getting the desired behavior can be done
by running $(go env GOROOT)/bin/go inside the x/build module, or simply
by running 'go' directly.

Change-Id: Ie1eec998e17b84adda0c3b3d3dc58e369f734d35
Reviewed-on: https://go-review.googlesource.com/c/build/+/657956
Reviewed-by: Cherry Mui <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>

Author: dmitshur

cmd/buildlet/Makefile

@@ -3,16 +3,13 @@
 #  - compile: build all buildlets (but do not upload)
 #  - upload: build and upload all buildlets to prod
 #  - dev-upload: build and upload all buildlets to dev cluster
-#  - install-go: install the version of Go needed by the Makefile
 #
 # Individual targets:
 #
 #  - buildlet.linux-amd64: build buildlet for linux-amd64 (but do not upload)
 #  - upload.linux-amd64: build buildlet for linux-amd64 and upload to prod
 #  - dev-upload.linux-amd64: build buildlet for linux-amd64 and upload to dev cluster
 
-GO=go1.22.8
-
 ALL=\
 	buildlet.aix-ppc64 \
 	buildlet.darwin-amd64 \
@@ -65,11 +62,6 @@ usage: FORCE
 
 FORCE:
 
-# A convenience for people who are missing $(GO).
-install-go:
-	go install golang.org/dl/$(GO)@latest
-	$(GO) download
-
 clean:
 	rm -f buildlet.*-*
 
@@ -80,7 +72,7 @@ GOFILES:=$(shell ls *.go)
 
 VERSION:=$(USER)-$(shell date -u +'%Y-%m-%dT%H:%M:%SZ')
 
-BUILD=CGO_ENABLED=0 $(GO) build -ldflags='-X main.Version=$(VERSION)' -o
+BUILD=CGO_ENABLED=0 go build -ldflags='-X main.Version=$(VERSION)' -o
 
 buildlet.%-386: $(GOFILES)
 	GOOS=$* GOARCH=386 $(BUILD) $@
@@ -145,7 +137,7 @@ buildlet.%-s390x: $(GOFILES)
 # Upload everything.
 upload: $(ALL:buildlet.%=upload.%)
 
-UPLOAD=$(GO) run golang.org/x/build/cmd/upload -verbose -public -cacheable=false
+UPLOAD=go run golang.org/x/build/cmd/upload -verbose -public -cacheable=false
 
 upload.%: buildlet.%
 	$(UPLOAD) -file=$< go-builder-data/$<

cmd/buildlet/stage0/Makefile

@@ -4,7 +4,6 @@
 #  - upload: build and upload all stage0 binaries to prod
 #  - dev-upload: build and upload all stage0 binaries to dev cluster
 #  - docker: build golang/buildlet-stage0 Docker image (but do not push)
-#  - install-go: install the version of Go needed by the Makefile
 #
 # Individual targets:
 #
@@ -19,8 +18,6 @@
 # automated VM/container creation scripts download them from.
 #
 
-GO=go1.19
-
 ALL=\
 	buildlet-stage0.illumos-amd64 \
 	buildlet-stage0.linux-arm \
@@ -43,11 +40,6 @@ usage: FORCE
 
 FORCE:
 
-# A convenience for people who are missing $(GO).
-install-go:
-	go install golang.org/dl/$(GO)@latest
-	$(GO) download
-
 clean:
 	rm -f buildlet-stage0.*-*
 
@@ -56,7 +48,7 @@ compile: $(ALL)
 
 GOFILES:=$(shell ls *.go)
 
-BUILD=CGO_ENABLED=0 $(GO) build -o
+BUILD=CGO_ENABLED=0 go build -o
 
 buildlet-stage0.%-arm: $(GOFILES)
 	GOOS=$* GOARCH=arm GOARM=7 $(BUILD) $@
@@ -98,7 +90,7 @@ docker: Dockerfile
 # Upload everything.
 upload: $(ALL:buildlet-stage0.%=upload.%)
 
-UPLOAD=$(GO) run golang.org/x/build/cmd/upload -verbose -public -cacheable=false
+UPLOAD=go run golang.org/x/build/cmd/upload -verbose -public -cacheable=false
 
 upload.%: buildlet-stage0.%
 	$(UPLOAD) -file=$< go-builder-data/$<