Re-commit r289955: [X86] Fold (setcc (cmp (atomic_load_add x, -C) C), COND) to...

Re-commit r289955: [X86] Fold (setcc (cmp (atomic_load_add x, -C) C), COND) to (setcc (LADD x, -C), COND) (PR31367)

This was reverted because it would miscompile code where the cmp had
multiple uses. That was due to a deficiency in the existing code, which
was fixed in r291630 (see the PR for details).

This re-commit includes an extra test for the kind of code that got
miscompiled: @test_sub_1_setcc_jcc.

llvm-svn: 291640