x86/Kconfig: Do not allow CONFIG_X86_X32_ABI=y with llvm-objcopy

x86/Kconfig: Do not allow CONFIG_X86_X32_ABI=y with llvm-objcopy

[ Upstream commit aaeed6ecc1253ce1463fa1aca0b70a4ccbc9fa75 ]

There are two outstanding issues with CONFIG_X86_X32_ABI and
llvm-objcopy, with similar root causes:

1. llvm-objcopy does not properly convert .note.gnu.property when going
   from x86_64 to x86_x32, resulting in a corrupted section when
   linking:

   https://github.com/ClangBuiltLinux/linux/issues/1141

2. llvm-objcopy produces corrupted compressed debug sections when going
   from x86_64 to x86_x32, also resulting in an error when linking:

   https://github.com/ClangBuiltLinux/linux/issues/514

After commit 41c5ef31ad71 ("x86/ibt: Base IBT bits"), the
.note.gnu.property section is always generated when
CONFIG_X86_KERNEL_IBT is enabled, which causes the first issue to become
visible with an allmodconfig build:

  ld.lld: error: arch/x86/entry/vdso/vclock_gettime-x32.o:(.note.gnu.property+0x1c): program property is too short

To avoid this error, do not allow CONFIG_X86_X32_ABI to be selected when
using llvm-objcopy. If the two issues ever get fixed in llvm-objcopy,
this can be turned into a feature check.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220314194842.3452-3-nathan@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>