s390: don't allow CONFIG_COMPAT with LD=ld.lld

s390: don't allow CONFIG_COMPAT with LD=ld.lld

When building 'ARCH=s390 defconfig compat.config' with GCC and
LD=ld.lld, there is an error when attempting to link the compat vDSO:

  ld.lld: error: unknown emulation: elf_s390
  make[4]: *** [arch/s390/kernel/vdso32/Makefile:48: arch/s390/kernel/vdso32/vdso32.so.dbg] Error 1

Much like clang, ld.lld only supports the 64-bit s390 emulation. Add a
dependency on not using LLD to CONFIG_COMPAT to avoid breaking the build
with this toolchain combination.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20240214-s390-compat-lld-dep-v1-1-abf1f4b5e514@kernel.org
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>