os: change UserHomeDir to use USERPROFILE on windows

Fixes #28182

Change-Id: I49c2117fba6325c234512f937ff2edfa9477f52f
Reviewed-on: https://go-review.googlesource.com/c/142886Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/file.go

@@ -384,12 +384,12 @@ func UserCacheDir() (string, error) {
 // UserHomeDir returns the current user's home directory.
 //
 // On Unix, including macOS, it returns the $HOME environment variable.
-// On Windows, it returns the concatenation of %HOMEDRIVE% and %HOMEPATH%.
+// On Windows, it returns %USERPROFILE%.
 // On Plan 9, it returns the $home environment variable.
 func UserHomeDir() string {
 	switch runtime.GOOS {
 	case "windows":
-		return Getenv("HOMEDRIVE") + Getenv("HOMEPATH")
+		return Getenv("USERPROFILE")
 	case "plan9":
 		return Getenv("home")
 	case "nacl", "android":