[kernel][phys] Remove arm64 LTO workaround

Building phys executables on arm64 with LTO was disabled
to work around compiler issues.  Remove that now that the
compiler issues have been addressed.

Fixed: 79992
Change-Id: Id2fe8197012b6aadeca49c92998fb5077b7f7bb0
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/693910
Reviewed-by: Joshua Seaton <joshuaseaton@google.com>
Fuchsia-Auto-Submit: Roland McGrath <mcgrathr@google.com>
Commit-Queue: Auto-Submit <auto-submit@fuchsia-infra.iam.gserviceaccount.com>