native shared libs in an SDK can be snapshotted

The snapshot script can now handle native shared libs in an SDK.

Bug: 138182343
Test: create following sdk module:
sdk {
    name: "mysdk",
    native_shared_libs: ["libc", "libdl"],
}
, then execute `m mysdk` and execute the update_prebuilt-1.sh as
prompted. Following directories are generated under the directory where
mysdk is defined at:

1
├── aidl
├── Android.bp
├── arm64
│   ├── include
│   ├── include_gen
│   └── lib
│       ├── libc.so
│       └── libdl.so
├── include
│   └── bionic
│       └── libc
│           └── include
│               ├── alloca.h
│               ├── android
│               │   ├── api-level.h
<omitted>

Change-Id: Ia1dcc5564c1cd17c6ccf441d06d5995af55db9ee
diff --git a/cc/library.go b/cc/library.go
index 1943e89..19a0787 100644
--- a/cc/library.go
+++ b/cc/library.go
@@ -158,6 +158,10 @@
 	// listed in local_include_dirs.
 	Export_include_dirs []string `android:"arch_variant"`
 
+	// list of directories that will be added to the system include path
+	// using -isystem for this module and any module that links against this module.
+	Export_system_include_dirs []string `android:"arch_variant"`
+
 	Target struct {
 		Vendor struct {
 			// list of exported include directories, like
@@ -245,10 +249,13 @@
 
 func (f *flagExporter) exportIncludes(ctx ModuleContext) {
 	f.dirs = append(f.dirs, f.exportedIncludes(ctx)...)
+	f.systemDirs = append(f.systemDirs, android.PathsForModuleSrc(ctx, f.Properties.Export_system_include_dirs)...)
 }
 
 func (f *flagExporter) exportIncludesAsSystem(ctx ModuleContext) {
+	// all dirs are force exported as system
 	f.systemDirs = append(f.systemDirs, f.exportedIncludes(ctx)...)
+	f.systemDirs = append(f.systemDirs, android.PathsForModuleSrc(ctx, f.Properties.Export_system_include_dirs)...)
 }
 
 func (f *flagExporter) reexportDirs(dirs ...android.Path) {
@@ -1280,7 +1287,7 @@
 
 var stubsVersionsLock sync.Mutex
 
-func latestStubsVersionFor(config android.Config, name string) string {
+func LatestStubsVersionFor(config android.Config, name string) string {
 	versions, ok := stubsVersionsFor(config)[name]
 	if ok && len(versions) > 0 {
 		// the versions are alreay sorted in ascending order