[clang] [compiler-rt] [llvm] [CMake][compiler-rt] Support for using compiler-rt atomic library (PR #106603)

[Petr Hosek via cfe-commits]

petrhosek wrote:

> Seems reasonable to me, I would wait for other approvals, as I'm relatively new here.
> 
> Just ensure this is good to go with rtsan, I recommend running the tests locally, as I don't think they're a part of the default pre-commit set
> 
> ```
> ninja check-rtsan
> ```

I'm seeing a test failure but I'm not sure if it's an issue with RTSan or compiler-rt atomic implementation:
```
FAIL: RealtimeSanitizer-Unit :: ./Rtsan-x86_64-Test/13/75 (1 of 84)
******************** TEST 'RealtimeSanitizer-Unit :: ./Rtsan-x86_64-Test/13/75' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/usr/local/google/home/phosek/llvm/llvm-project/build/fuchsia/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/compiler-rt/lib/rtsan/tests/./Rtsan-x86_64-Test-RealtimeSanitizer-Unit-1864241-13-75.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=75 GTEST_SHARD_INDEX=13 /usr/local/google/home/phosek/llvm/llvm-project/build/fuchsia/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/compiler-rt/lib/rtsan/tests/./Rtsan-x86_64-Test
--

Script:
--
/usr/local/google/home/phosek/llvm/llvm-project/build/fuchsia/runtimes/runtimes-x86_64-unknown-linux-gnu-bins/compiler-rt/lib/rtsan/tests/./Rtsan-x86_64-Test --gtest_filter=TestRtsan.AccessingALargeAtomicVariableDiesWhenRealtime
--
compiler-rt/lib/rtsan/tests/rtsan_test_utilities.h:40: Failure
Death test: RealtimeInvoke(std::forward<Function>(Func))
    Result: failed to die.
 Error msg:
[  DEATH   ] 


compiler-rt/lib/rtsan/tests/rtsan_test_utilities.h:40
Death test: RealtimeInvoke(std::forward<Function>(Func))
    Result: failed to die.
 Error msg:
[  DEATH   ] 



********************
********************
Failed Tests (1):
  RealtimeSanitizer-Unit :: ./Rtsan-x86_64-Test/TestRtsan/AccessingALargeAtomicVariableDiesWhenRealtime
```

https://github.com/llvm/llvm-project/pull/106603