meson: use the host architecture compiler/linker for src/boot/efi

meson: use the host architecture compiler/linker for src/boot/efi

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: b710072da441 ("add support for building efi modules")
(cherry picked from commit df7cacae696ae3c1d13d2f9a4db24815e07e29a1)

Gbp-Pq: Name meson-use-the-host-architecture-compiler-linker-for-src-b.patch