Test case fails but no assertion fails

**Describe the bug**

On the CI pipeline of one of my projects, I am experiencing a strange behaviour by Catch in a couple of tests: apparently, all ``REQUIRE()``s in all my ``TEST_CASE()``s pass, but one of the ``TEST_CASE()``s is marked as failing. See an example output here:

https://ci.appveyor.com/project/bluescarni/piranha-tng/builds/25230324/job/b2ymego1yi5kk852#L989

In the example above, the tests are run through CTest but the output and the result are identical if I run the offending executable manually: there is no information about what failed, and the exit status of the process is ``0``.

This happens *only* in a very specific case: a Windows build using ``clang-cl`` as a compiler, Visual Studio 2015 (as a standard library) and ``/std:c++17``. In the CI pipeline I have quite a few other build setups (MSVC 2019, Xcode, various versions of GCC/clang on ubuntu) and none of these builds exhibit the issue above. Some examples:

https://ci.appveyor.com/project/bluescarni/piranha-tng/builds/25230324/job/8drl58gx6gs5a832
https://travis-ci.org/bluescarni/piranha-tng/builds/544841099?utm_source=github_status&utm_medium=notification
https://circleci.com/gh/bluescarni/piranha-tng/1084?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

How could I debug what is going on?

Reproduce the failure with Catch2 under clang-cl, Visual Studio 2015, and /std:c++17, first running the offending executable directly and then through CTest. Compare the reported test result, output, and exit status with the working MSVC, Xcode, and GCC/Clang configurations. Done means identifying why the test is marked failed without an assertion failure and documenting or fixing that behavior.

Written by the indexing model from the issue text.