add new test file for nqp using perl

[tbrowder]

• provides a test harness for testing known failures
• test for known failure using =cut

[zoffixznet]

xt/ is generally for author tests while t/ is for user tests. This PR seems to be adding POD tests as author tests (is that necessary?) while at the same time it's adding author tests to be run with make test, along side user tests.

[tbrowder]

The test should be standard, but they use perl 5 so they need to be in a separate dir from the “exec nqp” tests. I forgot the special convention for xt, how about some other, unique dir then like “t/perl5/”?

[zoffixznet]

Personally, I'd just write the nqp version of STDERR capturing routine instead of writing an entire test file in Perl 5 just to execute a program that creates a file.

There is even already an implementation that can be adapted

[tbrowder]

I’ll close this and resubmit after we decide where to put the Perl 5 tests for .