objtool/klp: Rewrite symbol correlation algorithm

Rewrite the symbol correlation code, using a tiered list of
deterministic strategies in a loop.  For duplicately named symbols, each
tier applies a filter with the goal of finding a 1:1 deterministic
correlation between the original and patched version of the symbol.

The three matching strategies are:

  find_twin(): A funnel of progressively tighter filters.  Candidates
  with the same demangled name are counted at four levels: name, scope
  (local-vs-global), file (strict file association), and checksum
  (unchanged functions).  The widest level that yields a 1:1 match wins,
  narrower levels are only tried when the wider level is ambiguous.

  find_twin_suffixed(): Uses already-correlated LLVM symbol pairs to map
  .llvm.<hash> suffixes from orig to patched.  Because all promoted
  symbols from the same TU share the same hash, one correlated pair
  seeds the mapping for the entire TU.

  find_twin_positional(): Last resort, matches symbols by position among
  same-named candidates, similar to livepatch sympos.  Used for data
  objects like __quirk variables where no deterministic filter can
  distinguish the candidates.

Overall this works much better than the existing algorithm, particularly
with LTO kernels.

Acked-by: Song Liu <song@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

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