Add native_bridge target to Android.bp

This allows us to build guest libraries for the native bridge for
arm/arm64 architectures.

Bug: http://b/77159578
Test: make
Change-Id: I35520ca456105ddadd456c78a4eb1e6de39147c5
diff --git a/android/variable.go b/android/variable.go
index d29ba73..c500671 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -165,6 +165,16 @@
 	DeviceSecondaryCpuVariant  *string  `json:",omitempty"`
 	DeviceSecondaryAbi         []string `json:",omitempty"`
 
+	NativeBridgeArch        *string  `json:",omitempty"`
+	NativeBridgeArchVariant *string  `json:",omitempty"`
+	NativeBridgeCpuVariant  *string  `json:",omitempty"`
+	NativeBridgeAbi         []string `json:",omitempty"`
+
+	NativeBridgeSecondaryArch        *string  `json:",omitempty"`
+	NativeBridgeSecondaryArchVariant *string  `json:",omitempty"`
+	NativeBridgeSecondaryCpuVariant  *string  `json:",omitempty"`
+	NativeBridgeSecondaryAbi         []string `json:",omitempty"`
+
 	HostArch          *string `json:",omitempty"`
 	HostSecondaryArch *string `json:",omitempty"`