Touch output files in sbox

Some tools used by genrules set the timestamp of the generated file
to an old value.  For example, when using tar to extract files it
will set the timestamp of the extracted file to the value stored in
the tar file.  This can cause unnecessary rebuilds due to output files
that are older than their inputs.  Touch output files in sbox before
moving them into the output location.

Test: m checkbuild && m checkbuild
Change-Id: Idb0e71d2bf0ac3618338371132cc71be74bf9d9d

cmd/sbox/sbox.go

@@ -24,6 +24,7 @@ import (
 	"path"
 	"path/filepath"
 	"strings"
+	"time"
 )
 
 var (
@@ -265,6 +266,15 @@ func run() error {
 		if err != nil {
 			return err
 		}
+
+		// Update the timestamp of the output file in case the tool wrote an old timestamp (for example, tar can extract
+		// files with old timestamps).
+		now := time.Now()
+		err = os.Chtimes(tempPath, now, now)
+		if err != nil {
+			return err
+		}
+
 		err = os.Rename(tempPath, destPath)
 		if err != nil {
 			return err