[CI][C++] test-ubuntu-20.04-cpp-20 failure on AWS SDK

[pitrou]

Describe the bug, including details regarding any error messages, version, and platform.

See CI example:
https://github.com/ursacomputing/crossbow/actions/runs/5453237382/jobs/9921803828#step:6:1506

Excerpt:

-- Configuring incomplete, errors occurred!
See also "/build/cpp/awssdk_ep-prefix/src/awssdk_ep-build/CMakeFiles/CMakeOutput.log".
See also "/build/cpp/awssdk_ep-prefix/src/awssdk_ep-build/CMakeFiles/CMakeError.log".

-- stderr output is:
CMake Error at cmake/platform/linux.cmake:49 (message):
  Could not determine support for atomic operations.
Call Stack (most recent call first):
  CMakeLists.txt:173 (apply_post_project_platform_settings)



CMake Error at /build/cpp/awssdk_ep-prefix/src/awssdk_ep-stamp/awssdk_ep-configure-DEBUG.cmake:47 (message):
  Stopping after outputting logs.

Detailed CMake output from AWS SDK:

Performing C++ SOURCE FILE Test LIBATOMIC_EXISTS failed with the following output:
Change Dir: /build/cpp/awssdk_ep-prefix/src/awssdk_ep-build/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/ninja cmTC_0fd00 && [1/2] Building CXX object CMakeFiles/cmTC_0fd00.dir/src.cxx.o
FAILED: CMakeFiles/cmTC_0fd00.dir/src.cxx.o 
/usr/bin/c++    -fdiagnostics-color=always -fPIC -DLIBATOMIC_EXISTS -std=c++20 -o CMakeFiles/cmTC_0fd00.dir/src.cxx.o -c src.cxx
c++: error: unrecognized command line option '-std=c++20'; did you mean '-std=c++2a'?
ninja: build stopped: subcommand failed.


Source file was:

int main() {
    __atomic_load_8(nullptr, 0);
    return 0;
}

So it seems we're testing C++20 compatibility with a C++ compiler (/usr/bin/cc) that only has preliminary support for C++20 (it doesn't support -std=c++20).

Component(s)

C++, Continuous Integration