cmd/dist, cmd/internal/metadata: don't install metadata binary

It is only needed by cmd/dist, no need to build and install the
binary.

Change-Id: I6aba6b81496406077a0efba255c35020cff9d351
Reviewed-on: https://go-review.googlesource.com/c/go/+/411534
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>

src/cmd/dist/test.go

@@ -290,7 +290,7 @@ func (t *tester) maybeLogMetadata() error {
 	//
 	// TODO(prattmic): If we split dist bootstrap and dist test then this
 	// could be simplified to directly use internal/sysinfo here.
-	return t.dirCmd(filepath.Join(goroot, "src/cmd/internal/metadata"), "go", []string{"run", "."}).Run()
+	return t.dirCmd(filepath.Join(goroot, "src/cmd/internal/metadata"), "go", []string{"run", "main.go"}).Run()
 }
 
 // short returns a -short flag value to use with 'go test'

src/cmd/internal/metadata/main.go

@@ -5,6 +5,12 @@
 // Metadata prints basic system metadata to include in test logs. This is
 // separate from cmd/dist so it does not need to build with the bootstrap
 // toolchain.
+
+// This program is only used by cmd/dist. Add an "ignore" build tag so it
+// is not installed. cmd/dist does "go run main.go" directly.
+
+//go:build ignore
+
 package main
 
 import (