PR #628 exposes an underlying problem in roast

[tbrowder]

See PR #628 for a detailed description of a problem I had with the env var PERL6LIB and a Raku build used to test it.

Running a full spectest on the build with the PR failed when testing PERL6LIB every time even though the individual PERL6LIB test passes outside test harness. The file in question is 'S11-modules/perl6lib.t'.

The problem file is a revision of the original test. It was significantly changed from the original version at the suggestion of @ugexe in order to better conform with the recently reorganized roast testing aids including permanent modules for module testing.

To me it appears some bug in precompilation is triggered during this particular combination of files: The original test used a newly created module each time the test was run while the new test uses a static, existing module.

More information will be added here in a couple of days after I rerun the tests to collect more interim error messages.