VolumeManager: limit the scope of remountUid post fork.

We want to be sure we're not allocating memory, holding locks
or otherwise preventing the child process from making progress.

This is a temporary fix of limited scope. In the medium term, it
would be preferable to exec a binary that performs this work for us
as soon as we fork.

Test: manual
Bug: 141678467

Change-Id: I57dbd9b3c887aa27e2dd609abf0ad43c66f4ef2a
diff --git a/Android.bp b/Android.bp
index 5d93bfa..1c800fe 100644
--- a/Android.bp
+++ b/Android.bp
@@ -28,6 +28,7 @@
     name: "vold_default_libs",
 
     static_libs: [
+        "libasync_safe",
         "libavb",
         "libbootloader_message",
         "libdm",