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/toolchain_library.go b/cc/toolchain_library.go
index 0097ca3..2f3c9a1 100644
--- a/cc/toolchain_library.go
+++ b/cc/toolchain_library.go
@@ -53,12 +53,12 @@
 }
 
 func (library *toolchainLibraryDecorator) compile(ctx ModuleContext, flags Flags,
-	deps PathDeps) android.Paths {
-	return nil
+	deps PathDeps) Objects {
+	return Objects{}
 }
 
 func (library *toolchainLibraryDecorator) link(ctx ModuleContext,
-	flags Flags, deps PathDeps, objFiles android.Paths) android.Path {
+	flags Flags, deps PathDeps, objs Objects) android.Path {
 
 	libName := ctx.ModuleName() + staticLibraryExtension
 	outputFile := android.PathForModuleOut(ctx, libName)