Add ABFS (Android Build Filesystem) configuration option to Soong

Change-Id: Ibbe81004adc67b1212d7e619a35f7425bfee0d72
diff --git a/android/variable.go b/android/variable.go
index 3b02bc7..82dab4f 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -296,6 +296,7 @@
 	HostStaticBinaries           *bool    `json:",omitempty"`
 	Binder32bit                  *bool    `json:",omitempty"`
 	UseGoma                      *bool    `json:",omitempty"`
+	UseABFS                      *bool    `json:",omitempty"`
 	UseRBE                       *bool    `json:",omitempty"`
 	UseRBEJAVAC                  *bool    `json:",omitempty"`
 	UseRBER8                     *bool    `json:",omitempty"`