s390: link vmlinux with '-z notext'

ld.bfd defaults to '-z notext' (although it is customizable with the
'--enable-textrel-check' configure option) but ld.lld defaults to '-z
text', which causes issues with building the kernel due to the presence
of dynamic relocations in sections that are not writable.

  ld.lld: error: relocation R_390_64 cannot be used against local symbol; recompile with -fPIC

Add '-z notext' to avoid these errors, as this is expected, which
matches other architectures.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Tested-by: Justin Stitt <justinstitt@google.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Link: https://lore.kernel.org/r/20240207-s390-lld-and-orphan-warn-v1-11-8a665b3346ab@kernel.org


Signed-off-by: Heiko Carstens <hca@linux.ibm.com>