[llvm] [MC] Add support for -mcpu=native. (PR #159414)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-nvptx64-nvidia-ubuntu` running on `as-builder-7` while building `llvm` at step 6 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/160/builds/25227

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-llvm) failure: test (failure)
******************** TEST 'LLVM :: MC/AsmParser/native.s' FAILED ********************
Exit Code: -11

Command Output (stdout):
--
# RUN: at line 1
/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/bin/llvm-mc -filetype=obj -o /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/test/MC/AsmParser/Output/native.s.tmp -mcpu=native /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/test/MC/AsmParser/native.s 2> /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/test/MC/AsmParser/Output/native.s.tmp.stderr
# executed command: /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/bin/llvm-mc -filetype=obj -o /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/test/MC/AsmParser/Output/native.s.tmp -mcpu=native /home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/llvm-project/llvm/test/MC/AsmParser/native.s
# .---redirected output from '/home/buildbot/worker/as-builder-7/llvm-nvptx64-nvidia-ubuntu/build/test/MC/AsmParser/Output/native.s.tmp.stderr'
# | 'icelake-server' is not a recognized processor for this target (ignoring processor)
# | '+prfchw' is not a recognized feature for this target (ignoring feature)
# | '-cldemote' is not a recognized feature for this target (ignoring feature)
# | '+avx' is not a recognized feature for this target (ignoring feature)
# | '+aes' is not a recognized feature for this target (ignoring feature)
# | '+sahf' is not a recognized feature for this target (ignoring feature)
# | '+pclmul' is not a recognized feature for this target (ignoring feature)
# | '-xop' is not a recognized feature for this target (ignoring feature)
# | '+crc32' is not a recognized feature for this target (ignoring feature)
# | '-amx-fp8' is not a recognized feature for this target (ignoring feature)
# | '+xsaves' is not a recognized feature for this target (ignoring feature)
# | '-avx512fp16' is not a recognized feature for this target (ignoring feature)
# | '-usermsr' is not a recognized feature for this target (ignoring feature)
# | '-sm4' is not a recognized feature for this target (ignoring feature
# | ...
# `---data was truncated--------
# note: command had no output on stdout or stderr
# error: command failed with exit status: -11

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/159414