Avoid some MinGW test failures

Avoid some MinGW test failures

There were 4 classes of failure:

- line ending problems;
- unicode problems;
- file path munging problems; and
- a "hang" in test_cmp_http.

The unicode problems appear to be somewhere between wine or msys - they
don't actually appear to be a problem with the built binaries. We just skip
those tests for now.

Fixes #13558

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15939)