Add additional flag required for Flow Sensitive AFDO

It can be removed in the future once it becomes default.

Test: presubmit
Bug: 304282732
Change-Id: Ia7729593eff13ba5cc69fdb54519305295313b4d
diff --git a/cc/afdo.go b/cc/afdo.go
index 5c587c0..ac210d4 100644
--- a/cc/afdo.go
+++ b/cc/afdo.go
@@ -84,7 +84,10 @@
 		// 3. Make the profile searchable by the build system. So it's used the next time the binary
 		//	  is built.
 		flags.Local.CFlags = append([]string{"-funique-internal-linkage-names"}, flags.Local.CFlags...)
+		// Flags for Flow Sensitive AutoFDO
 		flags.Local.CFlags = append([]string{"-mllvm", "-enable-fs-discriminator=true"}, flags.Local.CFlags...)
+		// TODO(b/266595187): Remove the following feature once it is enabled in LLVM by default.
+		flags.Local.CFlags = append([]string{"-mllvm", "-improved-fs-discriminator=true"}, flags.Local.CFlags...)
 	}
 	if path := afdo.Properties.FdoProfilePath; path != nil {
 		// The flags are prepended to allow overriding.