[fbl] Backport AutoCall move-assignment fix from garnet Original fix: https://fuchsia-review.googlesource.com/c/garnet/+/160696 Change-Id: Ic4e5430600a8d6afa823eaf5effd3d714fbc0365
[zircon][mxtl->fbl] Rename mxtl to fbl Change-Id: Ie21b6498e1bfb0a7fa0315e40b9e5c3ee78646be