Better i386.inc:fpc_ansistr_unique.

Merge request out of this issue that makes fpc_ansistr_unique take 0 jumps in the common case of being a no-op. Can be rewritten using jmp if that bothers you, but I suppose shouldn’t?

Benchmark: noise. Okay, you might try UniqueStringBenchmark.pas that emulates a typical lazy scenario (possible outputs: (A) 1.7 before → 1.2 after, (B) 4.3 before → 3.3 after), but depending on the code layout you might not observe a speedup (in altered version I was getting 1.4 before → 1.4 after on the notebook (A)), so let’s settle on a speculative argument that not taking a jump is better than taking a jump.