Mark conscrypt-unbundled as enabled on Windows

As it's already being distributed in the Windows SDK as part of
apksigner, which has so far just been pulling the Linux jar files, but
I'm converting that build to Soong, so it'll have proper dependencies
now.

Bug: 187222815
Change-Id: I8bbcbc3b1039804727915829e9002fa558eb9d08
diff --git a/Android.bp b/Android.bp
index c0afb05..8e61ac4 100644
--- a/Android.bp
+++ b/Android.bp
@@ -523,6 +523,11 @@
     ],
     javacflags: ["-XDignore.symbol.file"],
     java_version: "1.8",
+    target: {
+        windows: {
+            enabled: true,
+        },
+    },
 }
 
 // Static unbundled Conscrypt crypto JNI library