[libc++] Temporarily mark tests as UNSUPPORTED to get the CI green

After recent changes to the Docker image, all hell broke loose and the
CI started failing. This patch marks a few tests as unsupported until
we can figure out what the issues are and fix them.

In the future, it would be ideal if the nodes could pick up the Dockerfile
present in the revision being tested, which would allow us to test changes
to the Dockerfile in the CI, like we do for all other code changes.

Differential Revision: https://reviews.llvm.org/D112737