[llvm] [tools][llc] Add `--save-stats` option (PR #163967)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-ubuntu-fast` running on `sie-linux-worker` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/39698

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: tools/llc/save-stats.ll' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 3
/home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/llc -mtriple=arm64-apple-macosx --save-stats=obj -o /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/test/tools/llc/Output/save-stats.ll.tmp.s /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/test/tools/llc/save-stats.ll && cat /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/test/tools/llc/Output/save-stats.ll.tmp.stats | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/test/tools/llc/save-stats.ll
# executed command: /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/llc -mtriple=arm64-apple-macosx --save-stats=obj -o /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/test/tools/llc/Output/save-stats.ll.tmp.s /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/llvm-project/llvm/test/tools/llc/save-stats.ll
# .---command stderr------------
# | /home/buildbot/buildbot-root/llvm-clang-x86_64-sie-ubuntu-fast/build/bin/llc: error: unable to get target for 'arm64-apple-macosx', see --version and --triple.
# `-----------------------------
# error: command failed with exit status: 1

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/163967