misc/dist: force modes to 0755 or 0644 in tarballs

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/5823045

misc/dist/bindist.go

@@ -536,6 +536,13 @@ func makeTar(targ, workdir string) error {
 		hdr.Uid = 0
 		hdr.Gid = 0
 
+		// Force mode to 0755 for executables, 0644 for everything else.
+		if hdr.Mode&0111 != 0 {
+			hdr.Mode = 0755
+		} else {
+			hdr.Mode = 0644
+		}
+
 		err = tw.WriteHeader(hdr)
 		if err != nil {
 			return fmt.Errorf("Error writing file %q: %v", name, err)