sparc: Disable compat support with LLD

An LLVM=1 sparc64 allmodconfig enables COMPAT and then tries to
build the 32-bit vDSO. That path cannot be linked with ld.lld:

  ld.lld: error: unknown emulation: elf32_sparc

ld.lld does not support the 32-bit SPARC ELF emulation used for
the compat vDSO, so keep COMPAT disabled when LLD is the linker.
This avoids selecting an unsupported build path while leaving the
existing GNU ld configuration unchanged.

Assisted-by: Codex:GPT-5.5
Signed-off-by: Rosen Penev <rosenp@gmail.com>
Acked-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Andreas Larsson <andreas@gaisler.com>
Link: https://lore.kernel.org/r/20260508000834.834824-1-rosenp@gmail.com
Signed-off-by: Andreas Larsson <andreas@gaisler.com>

Author: neheb

arch/sparc/Kconfig

@@ -450,6 +450,7 @@ endmenu
 config COMPAT
 	bool
 	depends on SPARC64
+	depends on !LD_IS_LLD
 	default y
 	select HAVE_UID16
 	select ARCH_WANT_OLD_COMPAT_IPC