[llvm] [MC] Early return on CPU help text invocation (PR #186663)

[via llvm-commits]

github-actions[bot] wrote:

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

* 171286 tests passed
* 3045 tests skipped
* 1 test failed

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

### LLVM
<details>
<summary>LLVM.tools/llvm-objdump/mattr-mcpu-help.test</summary>

```
Exit Code: -6

Command Output (stdout):
--
# RUN: at line 3
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/yaml2obj --docnum=1 /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/tools/llvm-objdump/mattr-mcpu-help.test -o /home/gha/actions-runner/_work/llvm-project/llvm-project/build/test/tools/llvm-objdump/Output/mattr-mcpu-help.test.tmp
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/yaml2obj --docnum=1 /home/gha/actions-runner/_work/llvm-project/llvm-project/llvm/test/tools/llvm-objdump/mattr-mcpu-help.test -o /home/gha/actions-runner/_work/llvm-project/llvm-project/build/test/tools/llvm-objdump/Output/mattr-mcpu-help.test.tmp
# note: command had no output on stdout or stderr
# RUN: at line 4
/home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/llvm-objdump -d /home/gha/actions-runner/_work/llvm-project/llvm-project/build/test/tools/llvm-objdump/Output/mattr-mcpu-help.test.tmp --mattr=help 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/tools/llvm-objdump/mattr-mcpu-help.test --check-prefixes=CHECK,CHECK-DISASSEMBLE
# executed command: /home/gha/actions-runner/_work/llvm-project/llvm-project/build/bin/llvm-objdump -d /home/gha/actions-runner/_work/llvm-project/llvm-project/build/test/tools/llvm-objdump/Output/mattr-mcpu-help.test.tmp --mattr=help
# note: command had no output on stdout or stderr
# error: command failed with exit status: -6
# 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/tools/llvm-objdump/mattr-mcpu-help.test --check-prefixes=CHECK,CHECK-DISASSEMBLE
# note: command had no output on stdout or stderr

--

```
</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/186663