cmd/dist: set buildvcs=false when building go-bootstrap

When building go-bootstrap as part of the make.bash process, the cmd/dist
invokes the bootstrap Go compiler to build the go_bootstrap tool:

${GOROOT_BOOTSTRAP}/bin/go install -tags=math_big_pure_go compiler_bootstrap purego bootstrap/cmd/...

If there is an invalid .git directory in a parent of ${GOROOT_BOOTSTRAP},
make.bash will fail. Reproduction of the issue:

  mkdir go-issue-61620
  cd ./go-issue-61620
  wget https://go.dev/dl/go1.19.11.src.tar.gz
  mkdir go-bootstrap
  tar -xf go1.19.11.src.tar.gz -C ./go-bootstrap --strip-components=1
  cd ./go-bootstrap/src/
  bash make.bash
  cd ../../
  wget https://go.dev/dl/go1.20.6.src.tar.gz
  mkdir go
  tar -xf go1.20.6.src.tar.gz -C ./go/ --strip-components=1
  printf "gitdir: ../../does/not/exist/.git" > ./.git
  cd ./go/src/
  GOROOT_BOOTSTRAP=$(pwd)/../../go-bootstrap/ bash make.bash

The build fails with the following error:

  Building Go toolchain1 using [snip]/go-1.19.10.
  error obtaining VCS status: exit status 128
    Use -buildvcs=false to disable VCS stamping.
  go tool dist: FAILED: [snip]/go-1.19.10/bin/go install -tags=math_big_pure_go \
    compiler_bootstrap purego bootstrap/cmd/...: exit status 1

This change unconditionally sets -buildvcs=false when compiling go-bootstrap. We
don't need the revision information in those binaries anyway. Setting this flag
was previously not done as we were unsure if the go-bootstrap compiler would be
new enough to support the buildvcs build flag. Since Go 1.20.x, Go 1.19.x is the
minimum version for go-bootstrap, and supports -buildvcs=false. We can now set
-buildvcs=false without worrying about compatibility.

Related: #54852
Fixes: #61620

Author: paralin

src/cmd/dist/buildtool.go

@@ -221,6 +221,9 @@ func bootstrapBuildTools() {
 	cmd := []string{
 		pathf("%s/bin/go", goroot_bootstrap),
 		"install",
+		// Fixes cases where an invalid .git is present in a parent of GOROOT_BOOTSTRAP.
+		// See: https://github.com/golang/go/issues/61620
+		"-buildvcs=false",
 		"-tags=math_big_pure_go compiler_bootstrap purego",
 	}
 	if vflag > 0 {