Add support for order-only dependencies to RuleBuilder

Test: TestRuleBuilder
Change-Id: I1609a790dd4d0a03c8308b6e552622fe33fa2499
Bug: 153071808
Merged-In: Icfa98d6840b1dc2e273ba29c33011635d1cf93b1
diff --git a/android/config.go b/android/config.go
index c9d7dab..a81b928 100644
--- a/android/config.go
+++ b/android/config.go
@@ -570,8 +570,8 @@
 	return String(c.productVariables.BuildId)
 }
 
-func (c *config) BuildNumberFromFile() string {
-	return String(c.productVariables.BuildNumberFromFile)
+func (c *config) BuildNumberFile(ctx PathContext) Path {
+	return PathForOutput(ctx, String(c.productVariables.BuildNumberFile))
 }
 
 // DeviceName returns the name of the current device target