cmd/go/internal/vgo: print auto-guessed module setting during go.mod init

Printing the auto-guessed module setting when go.mod file is not present,
so that if it's wrong the user may avoid a debugging session.

Fixes golang/go#23978

Change-Id: I2f07d2e0a517598277a8e636e751ea640d5ca63a
Reviewed-on: https://go-review.googlesource.com/114155
Reviewed-by: Russ Cox <rsc@golang.org>

vendor/cmd/go/internal/vgo/init.go

diff --git a/vendor/cmd/go/internal/vgo/init.go b/vendor/cmd/go/internal/vgo/init.go
index 2c8b41a..13b5a68 100644
--- a/vendor/cmd/go/internal/vgo/init.go
+++ b/vendor/cmd/go/internal/vgo/init.go
@@ -159,6 +159,7 @@
 	if err != nil {
 		base.Fatalf("vgo: %v", err)
 	}
+	fmt.Fprintf(os.Stderr, "vgo: module %s\n", path)
 	modFile = new(modfile.File)
 	modFile.AddModuleStmt(path)
 	Target = module.Version{Path: path}