[libc++] [test] UNSUPPORTED my new uniform_int_distribution test on MinGW.

After 9fe67486, this test fails on MinGW for some reason.
https://buildkite.com/llvm-project/libcxx-ci/builds/7922#9e267294-441d-4b79-8a19-30fdb5599c1f
All it says in the build output is

    note: command had no output on stdout or stderr
    error: command failed with exit status: 4294967295