Add overrides support for snapshots

Overrides properties will now be captured in json flag files, which will
be copied to installed vendor snapshot modules.

Bug: 216567575
Test: soong test && manual install
Change-Id: Ife5e84b126e798fba7802b9cff000c9197756cb9
diff --git a/cc/vendor_snapshot.go b/cc/vendor_snapshot.go
index 77e6f6f..2dcf26e 100644
--- a/cc/vendor_snapshot.go
+++ b/cc/vendor_snapshot.go
@@ -239,6 +239,9 @@
 		}
 		prop.RuntimeLibs = m.SnapshotRuntimeLibs()
 		prop.Required = m.RequiredModuleNames()
+		if o, ok := m.(overridable); ok {
+			prop.Overrides = o.overriddenModules()
+		}
 		for _, path := range m.InitRc() {
 			prop.InitRc = append(prop.InitRc, filepath.Join("configs", path.Base()))
 		}