Mark libziparchive vendor_available.

libziparchive is a library which belongs to vndk-cap. Mark it
vendor_available to enable header-abi-dumper's invocation to identify it
as a part of the vndk.

Details: https://android-review.googlesource.com/368372

Test: mm -j64

Bug: 38244611

Change-Id: Ibe490cc6c2cfca0f8d58df45317bb3a491d530f0

libziparchive/Android.bp

@@ -56,6 +56,8 @@ cc_defaults {
 cc_library {
     name: "libziparchive",
     host_supported: true,
+    vendor_available:true,
+
     defaults: ["libziparchive_defaults", "libziparchive_flags"],
     shared_libs: ["liblog", "libbase"],
     target: {