Add comment for afdo flag

Change-Id: If80df0ac0527784b13158325589c29587db8d5f9
Test: N/A
diff --git a/cc/afdo.go b/cc/afdo.go
index 137ea97..bc7cd52 100644
--- a/cc/afdo.go
+++ b/cc/afdo.go
@@ -34,7 +34,8 @@
 
 var afdoProfileProjectsConfigKey = android.NewOnceKey("AfdoProfileProjects")
 
-const afdoCFlagsFormat = "-fprofile-sample-use=%s"
+// This flag needs to be in both CFlags and LdFlags to ensure correct symbol ordering
+const afdoFlagsFormat = "-fprofile-sample-use=%s"
 
 func recordMissingAfdoProfileFile(ctx android.BaseModuleContext, missing string) {
 	getNamedMapForConfig(ctx.Config(), modulesMissingProfileFileKey).Store(missing, true)
@@ -86,7 +87,7 @@
 	}
 	if path := afdo.Properties.FdoProfilePath; path != nil {
 		// The flags are prepended to allow overriding.
-		profileUseFlag := fmt.Sprintf(afdoCFlagsFormat, *path)
+		profileUseFlag := fmt.Sprintf(afdoFlagsFormat, *path)
 		flags.Local.CFlags = append([]string{profileUseFlag}, flags.Local.CFlags...)
 		flags.Local.LdFlags = append([]string{profileUseFlag, "-Wl,-mllvm,-no-warn-sample-unused=true"}, flags.Local.LdFlags...)