Add some real EBCDIC testing

[NWilson]

Part of #655

We currently don't have any testing in CI whatsoever for the EBCDIC code. I know it's obscure, but I feel it ought be tested at least a little before we put out a release.

I'm making it so that you can now compile a version of the PCRE2 libraries which fully-support EBCDIC, on any platform, with any compiler.

This lets us now write some proper EBCDIC tests and run them in CI.

[NWilson]

I've been undecided about what's the best test suite to run on the EBCDIC build.

Here's my decision: I want to run the full test suite (1 to 27), but obviously there will be some failures. I'll introduce a new "#ifndef EBCDIC" directive in the test input/output files, to mask out the specific tests that fail in EBCDIC mode. These will be ones of the form does [\x10-\x60] match 'A' and similar things.

I basically don't want to add a new "testoutputN-EBC" for every testoutput file (too verbose when writing tests). Nor do I want to just skip all the existing tests. Nor can we somehow maintain a list of "expected failures" under EBCDIC.

I'll also rename the existing "testinputEBC" to "testinput28" and just make it conditional the EBCDIC build, in the same way that lots of existing tests are conditional on build properties.

[zherczeg]

Is it possible to really test EBCDIC on ASCII? I hope this will not make our life difficult.

[NWilson]

Yes, it's totally possible. It's in the PR currently, I just haven't updated the RunTest script to get all the tests passing.

It's also necessary to test the EBCDIC code - I just don't feel comfortable shipping lines of code that we haven't compiled or tested.