boot: Only build with debug symbols in developer mode

boot: Only build with debug symbols in developer mode

The debug symbols are of very limited use in proper deployments
unlike with regular userspace. Unless someone goes through the pain
of setting up an EFI debugger (assuming their firmware even supports
this in the first place) any provided debug symbols will just be
useless.
Debugging under QEMU is possible, but even then it is non-trivial
to set up, so anyone willing to go that far can just build in
developer mode.

Meanwhile, at least x86 firmware tends to refuse binaries that contain
debug symbols. We do strip the files when converted to PE anyway, but
the elf file needs to stay around on other arches as objcopy does not
support PE as input there.

Also, the generated debug symbols seem to be not reproducible when
building with LTO. Whether this is an issue in tooling or our side
is unclear. This works around this issue.

Fixes: #22157