Mark cc_library_headers targets as being bp2build_available.

Test: build/bazel/scripts/bp2build-sync.sh write.
Change-Id: I78a491d20779f50757b55c8e5305b588bf613839
diff --git a/libc/async_safe/Android.bp b/libc/async_safe/Android.bp
index 66389b9..222d9f6 100644
--- a/libc/async_safe/Android.bp
+++ b/libc/async_safe/Android.bp
@@ -47,4 +47,5 @@
         "//apex_available:platform",
         "com.android.runtime",
     ],
+    bazel_module: { bp2build_available: true },
 }