[llvm] [X86][MC] Check AdSize16 for 16-bit addressing (PR #99761)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-sve-vla` running on `linaro-g3-04` while building `llvm` at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/17/builds/1094

Here is the relevant piece of the build log for the reference:
```
Step 7 (ninja check 1) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
...
PASS: lit :: shtest-recursive-substitution.py (91360 of 91370)
PASS: lit :: allow-retries.py (91361 of 91370)
PASS: lit :: shtest-external-shell-kill.py (91362 of 91370)
PASS: lit :: discovery.py (91363 of 91370)
PASS: lit :: googletest-timeout.py (91364 of 91370)
PASS: lit :: selecting.py (91365 of 91370)
PASS: lit :: shtest-timeout.py (91366 of 91370)
PASS: lit :: max-time.py (91367 of 91370)
PASS: lit :: shtest-shell.py (91368 of 91370)
PASS: lit :: shtest-define.py (91369 of 91370)
command timed out: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1690.067624

```

https://github.com/llvm/llvm-project/pull/99761