Handle product vars *flags props in cc* modules

Test: build/bazel/ci/bp2build.sh
Bug: 188497994
Change-Id: Ifb379e370075d6a7bc55b82d79c210c31ef377e9
diff --git a/bazel/properties.go b/bazel/properties.go
index b9d6ead..4cae21e 100644
--- a/bazel/properties.go
+++ b/bazel/properties.go
@@ -993,6 +993,6 @@
 // TryVariableSubstitution, replace string substitution formatting within s with Starlark
 // string.format compatible tag for productVariable.
 func TryVariableSubstitution(s string, productVariable string) (string, bool) {
-	sub := productVariableSubstitutionPattern.ReplaceAllString(s, "{"+productVariable+"}")
+	sub := productVariableSubstitutionPattern.ReplaceAllString(s, "$("+productVariable+")")
 	return sub, s != sub
 }