Create dexpreopt install dir

If dexpreopt is disabled inside dexpreopt_gen there won't be any installed files and the install directory won't be created, causing soong_zip to fail.  Create the directory ahead of time.

Test: treehugger
Change-Id: Icf17d0bcd617eeeafdcd50ab56359fa8d6612822

dexpreopt/dexpreopt_gen/dexpreopt_gen.go

@@ -104,6 +104,7 @@ func writeScripts(global dexpreopt.GlobalConfig, module dexpreopt.ModuleConfig,
 	installDir := filepath.Join(filepath.Dir(module.BuildPath), "dexpreopt_install")
 
 	dexpreoptRule.Command().FlagWithArg("rm -rf ", installDir)
+	dexpreoptRule.Command().FlagWithArg("mkdir -p ", installDir)
 
 	for _, install := range dexpreoptRule.Installs() {
 		installPath := filepath.Join(installDir, install.To)