Generate linker config with packaged items.

Previously, we gather all deps without checking if a dep is actually one
of packaged items (CopyDepsToZip contents)

For example, following items shouldn't be listed.

provideLibs: "platform-mainline-sdk_libartpalette-system@current.so"
provideLibs: "platform-mainline-sdk_liblog@current.so"
provideLibs: "runtime-module-sdk_libc@current.so"
provideLibs: "runtime-module-sdk_libdl@current.so"
provideLibs: "runtime-module-sdk_libdl_android@current.so"
provideLibs: "runtime-module-sdk_libm@current.so"

Now, we gather only those modules contributing CopyDepsToZip to generate
linker config for android_system_image.

Test: m nothing
Test: m microdroid
Test: conv_linker_config print -s
    .../microdroid/android_common/root/system/etc/linker.config.pb
    shouldn't list sdk members.
Change-Id: Ife5d2193ab59970367d10e196aaaa922c6582862
diff --git a/android/packaging.go b/android/packaging.go
index 72c0c17..9065826 100644
--- a/android/packaging.go
+++ b/android/packaging.go
@@ -198,8 +198,8 @@
 	}
 }
 
-// See PackageModule.CopyDepsToZip
-func (p *PackagingBase) CopyDepsToZip(ctx ModuleContext, zipOut WritablePath) (entries []string) {
+// Returns transitive PackagingSpecs from deps
+func (p *PackagingBase) GatherPackagingSpecs(ctx ModuleContext) map[string]PackagingSpec {
 	m := make(map[string]PackagingSpec)
 	ctx.VisitDirectDeps(func(child Module) {
 		if pi, ok := ctx.OtherModuleDependencyTag(child).(PackagingItem); !ok || !pi.IsPackagingItem() {
@@ -211,7 +211,12 @@
 			}
 		}
 	})
+	return m
+}
 
+// See PackageModule.CopyDepsToZip
+func (p *PackagingBase) CopyDepsToZip(ctx ModuleContext, zipOut WritablePath) (entries []string) {
+	m := p.GatherPackagingSpecs(ctx)
 	builder := NewRuleBuilder(pctx, ctx)
 
 	dir := PathForModuleOut(ctx, ".zip")