Do not fail EFI build with newer binutils

Do not fail EFI build with newer binutils

Newer binutils versions currently trigger the following warnings due to
a bug in gnu-efi

on arm64:
/usr/bin/ld.bfd: warning: src/boot/efi/systemd-bootaa64.elf has a LOAD segment with RWX permissions

on amd64:
/usr/bin/ld.bfd: warning: /usr/lib/crt0-efi-x86_64.o: missing .note.GNU-stack section implies executable stack

This results in a build failure due to --fatal-warnings.
Work around this issue by suppressing those warnings until gnu-efi has
been fixed.

See https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1013341