Fix EFI loader reproducibility with lld
When the various loaders under stand/efi are built, the resulting
binaries differ over multiple runs, even if WITH_REPRODUCIBLE_BUILD is
used. This is caused by lld multithreading and the custom linker scripts
for the loaders, and affects the following binaries:
- loader_4th.efi
- loader_4th.sym
- loader_4th.sym.full
- loader_lua.efi
- loader_lua.sym
- loader_lua.sym.full
- loader_simp.efi
- loader_simp.sym
- loader_simp.sym.full
Work around this by disabling lld threading for these binaries.
Reviewed by: emaste
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D46271