Start using "struct Objects" to store object Paths

So that we can represent other files that get generated along with the
objects, like the gcno coverage information, and per-file clang-tidy
runs.

Test: Soong's build.ninja identical before/after
Change-Id: I5c553a153c436d5403549f62c73fe79c5f101779
diff --git a/cc/prebuilt.go b/cc/prebuilt.go
index 55775b6..4328df8 100644
--- a/cc/prebuilt.go
+++ b/cc/prebuilt.go
@@ -46,7 +46,7 @@
 }
 
 func (p *prebuiltLibraryLinker) link(ctx ModuleContext,
-	flags Flags, deps PathDeps, objFiles android.Paths) android.Path {
+	flags Flags, deps PathDeps, objs Objects) android.Path {
 	// TODO(ccross): verify shared library dependencies
 	if len(p.Prebuilt.Properties.Srcs) > 0 {
 		p.libraryDecorator.exportIncludes(ctx, "-I")