[llvm] [AArch64] support `.arch_extension dit` (PR #169999)

[via llvm-commits]

github-actions[bot] wrote:

<!--PREMERGE ADVISOR COMMENT: Linux-->
# :penguin: Linux x64 Test Results

* 166633 tests passed
* 2897 tests skipped
* 1 test failed

## Failed Tests
(click on a test name to see its output)

### LLVM
<details>
<summary>LLVM.MC/AArch64/armv8.3a-complex_missing.s</summary>

```
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 1
not /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+v8.3a,-complxnum,+fullfp16 -o - /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s 2>&1 | /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/FileCheck /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s
# executed command: not /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/llvm-mc -triple aarch64-none-linux-gnu -show-encoding -mattr=+v8.3a,-complxnum,+fullfp16 -o - /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s
# note: command had no output on stdout or stderr
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/FileCheck /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s
# .---command stderr------------
# | /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s:28:10: error: CHECK: expected string not found in input
# | //CHECK: {{.*}} error: instruction requires: complxnum
# |          ^
# | <stdin>:1:1: note: scanning from here
# | /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s:3:1: error: instruction requires: fcma
# | ^
# | <stdin>:1:108: note: possible intended match here
# | /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s:3:1: error: instruction requires: fcma
# |                                                                                                            ^
# | 
# | Input file: <stdin>
# | Check file: /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s
# | 
# | -dump-input=help explains the following input dump.
# | 
# | Input was:
# | <<<<<<
# |             1: /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s:3:1: error: instruction requires: fcma 
# | check:28'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
# | check:28'1                                                                                                                ?                                     possible intended match
# |             2: fcmla v0.4h, v1.4h, v2.4h, #0 
# | check:28'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |             3: ^ 
# | check:28'0     ~~
# |             4: /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/MC/AArch64/armv8.3a-complex_missing.s:4:1: error: instruction requires: fcma 
# | check:28'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |             5: fcmla v0.8h, v1.8h, v2.8h, #0 
# | check:28'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# |             6: ^ 
# | check:28'0     ~~
# |             .
# |             .
# |             .
# | >>>>>>
# `-----------------------------
# error: command failed with exit status: 1

--

```
</details>

If these failures are unrelated to your changes (for example tests are broken or flaky at HEAD), please open an issue at https://github.com/llvm/llvm-project/issues and add the `infrastructure` label.

https://github.com/llvm/llvm-project/pull/169999