[libcxxabi] [llvm] [clang] [openmp] [compiler-rt] [libcxx] [mlir] [lld] [runtimes] Use LLVM libunwind from libc++abi by default (PR #77687)

[Fangrui Song via cfe-commits]

MaskRay wrote:

> @ldionne @MaskRay Any ideas what does this mean [lab.llvm.org/buildbot/#/builders/85/builds/21530](https://lab.llvm.org/buildbot/#/builders/85/builds/21530)

This looks like a fatal runtime error for the test `test/ExecutionEngine/MCJIT/Output/eh.ll` related to OrcJIT. It seems unrelated to `compiler-rt/lib/orc/elfnix_platform.cpp`. I think it is perhaps related to existing OrcJIT instability, happened to be uncovered by this CMake change.
```
GTEST_OUTPUT=json:/b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/unittests/Interpreter/ExceptionTests/./ClangReplInterpreterExceptionTests-Clang-Unit-2380782-0-1.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=1 GTEST_SHARD_INDEX=0 /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm_build_ubsan/tools/clang/unittests/Interpreter/ExceptionTests/./ClangReplInterpreterExceptionTests
--
[==========] Running 1 test from 1 test suite.
[----------] Global test environment set-up.
[----------] 1 test from InterpreterTest
[ RUN      ] InterpreterTest.CatchException
libunwind: __unw_add_dynamic_fde: bad fde: FDE is really a CIE
libc++abi: terminating due to uncaught exception of type custom_exception
 #0 0x000055c0558128ce llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Unix/Signals.inc:723:13
 #1 0x000055c05580f716 llvm::sys::RunSignalHandlers() /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Signals.cpp:106:18
 #2 0x000055c05581333f SignalHandler(int) /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/llvm/lib/Support/Unix/Signals.inc:413:1
 #3 0x00007fac4963c460 (/lib/x86_64-linux-gnu/libc.so.6+0x3c460)
 #4 0x00007fac4969152b pthread_kill (/lib/x86_64-linux-gnu/libc.so.6+0x9152b)
 #5 0x00007fac4963c3b6 raise (/lib/x86_64-linux-gnu/libc.so.6+0x3c3b6)
 #6 0x00007fac4962287c abort (/lib/x86_64-linux-gnu/libc.so.6+0x2287c)
 #7 0x00007fac499d0edb abort_message /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/abort_message.cpp:78:5
 #8 0x00007fac499a43c6 demangling_terminate_handler() /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_default_handlers.cpp:77:9
 #9 0x00007fac499cf812 std::__terminate(void (*)()) /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_handlers.cpp:61:9
#10 0x00007fac499d9ba7 __cxxabiv1::failed_throw(__cxxabiv1::__cxa_exception*) /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_exception.cpp:152:5
#11 0x00007fac499d9761 cxa_exception_from_thrown_object /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_exception.cpp:45:57
#12 0x00007fac499d9761 __cxa_throw /b/sanitizer-x86_64-linux-bootstrap-ubsan/build/llvm-project/libcxxabi/src/cxa_exception.cpp:264:41
#13 0x00007fac49cc40f9 
```

https://github.com/llvm/llvm-project/pull/77687