internal/crosscompile:Oz optimize level for embed target

internal/crosscompile/crosscompile.go

@@ -481,9 +481,8 @@ func UseTarget(targetName string) (export Export, err error) {
 	envs := buildEnvMap(env.LLGoROOT())
 
 	// Convert LLVMTarget, CPU, Features to CCFLAGS/LDFLAGS
-	var ccflags []string
 	var ldflags []string
-
+	ccflags := []string{"-Oz"}
 	cflags := []string{"-Wno-override-module", "-Qunused-arguments", "-Wno-unused-command-line-argument"}
 	if config.LLVMTarget != "" {
 		cflags = append(cflags, "--target="+config.LLVMTarget)