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Bernardo reported an error that Nathan bisected down to
(x86_64) defconfig+LTO_CLANG_FULL+X86_PMEM_LEGACY.

    LTO     vmlinux.o
  ld.lld: error: <instantiation>:1:13: redefinition of 'found'
  .set found, 0
              ^

  <inline asm>:29:1: while in macro instantiation
  extable_type_reg reg=%eax, type=(17 | ((0) << 16))
  ^

This appears to be another LTO specific issue similar to what was folded
into commit 4b5305de ("x86/extable: Extend extable functionality"),
where the `.set found, 0` in DEFINE_EXTABLE_TYPE_REG in
arch/x86/include/asm/asm.h conflicts with the symbol for the static
function `found` in arch/x86/kernel/pmem.c.

Assembler .set directive declare symbols with global visibility, so the
assembler may not rename such symbols in the event of a conflict. LTO
could rename static functions if there was a conflict in C sources, but
it cannot see into symbols defined in inline asm.

The symbols are also retained in the symbol table, rega...