[llvm] MCInst: decrease inline element count to 6. NFC (PR #94913)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> @MaskRay That's probably just noise. But you can see some statistically significant results here: [llvm-compile-time-tracker.com/compare.php?from=f7ccb320859b9e341f74dc0cd7791a3b871eb937&to=ed52b7b350213ed3731109ac3c2a777f452df706&stat=max-rss&linkStats=on](https://llvm-compile-time-tracker.com/compare.php?from=f7ccb320859b9e341f74dc0cd7791a3b871eb937&to=ed52b7b350213ed3731109ac3c2a777f452df706&stat=max-rss&linkStats=on) See the green "stage1-ReleaseLTO-g (link only)" numbers. (LTO link-only numbers are usually best for looking at memory usage, esp. for the backend.)

Thanks for the `&linkStats=on` trick and the tool!

https://github.com/llvm/llvm-project/pull/94913