cross building systemd to arm64 presently fails, because the build
system uses plain gcc and plain ld (build architecture compiler and
linker respectively) for building src/boot/efi. These values come from
the efi-cc and efi-ld options respectively. It rather should be using
host tools here.
Fixes: b710072da4 ("add support for building efi modules")
Helmut Grohne