Merge changes from topic 'system-vendor-internal-pick'

* changes:
  libbase: fix build breakage
  libsync: vendor_available
  Remove VNDK warning.
  libbase: make vendor_available
  libcutils: vendor_available
  libbacktrace: make vendor_available
  libbase: add libbase_headers

Cr-Mirrored-From: https://chromium.googlesource.com/aosp/platform/system/core
Cr-Mirrored-Commit: 3dfaa4449136bb48b504a9d39e380e7665acf3d1
diff --git a/Android.bp b/Android.bp
index a4e5599..4bafb08 100644
--- a/Android.bp
+++ b/Android.bp
@@ -8,6 +8,7 @@
 
 cc_library_shared {
     name: "libsync",
+    vendor_available: true,
     defaults: ["libsync_defaults"],
 }