[llvm] [MC, X86] emitInstruction: remove virtual function calls due to Intel JCC Erratum (PR #96835)

[Fangrui Song via llvm-commits]

MaskRay wrote:

https://llvm-compile-time-tracker.com/compare.php?from=4558e45e7e33d1cfc1a54af761085e358dbab64b&to=1a702c28cba578bbc594d06e40dce096500fe08d&stat=instructions:u

stage2-O3:

|Benchmark|Old|New|
|--- |--- |--- |
|kimwitu++|38987M|38942M (-0.12%)|
|sqlite3|35149M|35134M (-0.04%)|
|consumer-typeset|31961M|31951M (-0.03%)|
|Bullet|93293M|93203M (-0.10%)|
|tramp3d-v4|78572M|78510M (-0.08%)|
|mafft|32958M|32946M (-0.03%)|
|ClamAV|50424M|50404M (-0.04%)|
|lencod|61201M|61193M (-0.01%)|
|SPASS|43001M|42968M (-0.08%)|
|7zip|191976M|191913M (-0.03%)|
|geomean|55343M|55312M (-0.06%)|


https://github.com/llvm/llvm-project/pull/96835