Revert "Roll clang and buildroot"

[zanderso]

Reverts #33284

The roll to the framework is failing: flutter/flutter#103672

[zanderso]

It looks like flutter_tester is failing with:

Shell: [ERROR:flutter/runtime/dart_vm_data.cc(18)] VM snapshot invalid and could not be inferred from settings.
Shell: [ERROR:flutter/runtime/dart_vm.cc(269)] Could not set up VM data to bootstrap the VM from.
Shell: [ERROR:flutter/runtime/dart_vm_lifecycle.cc(84)] Could not create Dart VM instance.
Shell: [FATAL:flutter/shell/common/shell.cc(143)] Check failed: vm. Must be able to initialize the VM.

But only on mac.

[dnfield]

Seems really strange that it didn't fail on the engine CI host tests using flutter_tester...

[zanderso]

@dnfield on CI, we only run the 'dart' test suite of run_tests.py using a host_debug_unopt build on mac, and it looks like the issue is that the Dart snapshot symbols (e.g. _kDartSnapshotData, etc.) in flutter_tester are getting dropped by the new linker in non-_unopt builds (but only on mac).