Mark libdemangle as vendor_available

The lib is used by libc_malloc_debug_backtrace which is
vendor_available. libc_malloc_debug_backtrace is marked as such because
it is again used by libmemunreachable which is vendor_available.

Bug: 33241851
Test: BOARD_VNDK_VERSION=current m -j libmemunreachable.vendor
Change-Id: I978f8e34d354e4fe03a3c19dd0dbc6899f26a793
diff --git a/demangle/Android.bp b/demangle/Android.bp
index 96ab57d..e55c886 100644
--- a/demangle/Android.bp
+++ b/demangle/Android.bp
@@ -29,6 +29,7 @@
 cc_library {
     name: "libdemangle",
     defaults: ["libdemangle_defaults"],
+    vendor_available: true,
 
     srcs: [
         "Demangler.cpp",