*: Fix build and readme in llvm17

[breezewish]

What problem does this PR solve?

Issue Number: ref https://github.com/pingcap/tiflash/issues/6233

Problem Summary:

What is changed and how it works?

Fix README instruction for MacOS
Fix build unit test failure in LLVM17 + MacOS

This doesn't work, so removed: "use CMAKE_C_COMPILER and CMAKE_CXX_COMPILER to specify the compiler"

Check List

Tests

• [ ] Unit test
• [ ] Integration test
• [x] Manual test (add detailed scripts or steps below)
• [ ] No code

Side effects

• [ ] Performance regression: Consumes more CPU
• [ ] Performance regression: Consumes more Memory
• [ ] Breaking backward compatibility

Documentation

• [ ] Affects user behaviors
• [ ] Contains syntax changes
• [ ] Contains variable changes
• [ ] Contains experimental features
• [ ] Changes MySQL compatibility

Release note

None

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JaySon-Huang, Lloyd-Pottiger

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/pingcap/tiflash/blob/master/OWNERS)~~ [JaySon-Huang,Lloyd-Pottiger] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-11-20 03:15:19.060098279 +0000 UTC m=+1506.679752795: :ballot_box_with_check: agreed by Lloyd-Pottiger.
• 2024-11-20 03:32:13.272078789 +0000 UTC m=+2520.891733305: :ballot_box_with_check: agreed by JaySon-Huang.

[JinheLin]

/retest

[ti-chi-bot[bot]]

@breezewish: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

trigger some heavy tests which will not run always when PR updated.

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

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[JaySon-Huang]

happen to unstable test: https://github.com/pingcap/tiflash/issues/9662

[JaySon-Huang]

/test pull-unit-test