Fix generated headers of snapshot

For VNDK snapshot and SDK snapshot, deps files have been used to capture
generated headers. But exported deps might contain intermediate phony
files instead of actual header files, which are for optimization of
ninja. To correctly capture all headers, exported generated header files
are gathered separately.

Bug: 65377115
Test: m nothing
Change-Id: Ia03fa69186490a818578190e3c0bfb0261d1fd6e
diff --git a/cc/prebuilt.go b/cc/prebuilt.go
index 4e6cdd7..32676d6 100644
--- a/cc/prebuilt.go
+++ b/cc/prebuilt.go
@@ -90,6 +90,7 @@
 		p.libraryDecorator.reexportSystemDirs(deps.ReexportedSystemDirs...)
 		p.libraryDecorator.reexportFlags(deps.ReexportedFlags...)
 		p.libraryDecorator.reexportDeps(deps.ReexportedDeps...)
+		p.libraryDecorator.addExportedGeneratedHeaders(deps.ReexportedGeneratedHeaders...)
 
 		builderFlags := flagsToBuilderFlags(flags)