Mark lib_async_safe_headers as supporting linux_bionic

This target is needed by linux_bionic targets and so should support
it.

Test: ./art/tools/build_linux_bionic.sh com.android.runtime.host
Change-Id: Ib12f1cf1d70e606b0921f507b3e460f5d543017e
diff --git a/libc/async_safe/Android.bp b/libc/async_safe/Android.bp
index 6ae1c42..fbaaad1 100644
--- a/libc/async_safe/Android.bp
+++ b/libc/async_safe/Android.bp
@@ -22,6 +22,7 @@
 cc_library_headers {
     name: "libasync_safe_headers",
     recovery_available: true,
+    defaults: ["linux_bionic_supported"],
 
     export_include_dirs: ["include"],