Build tests-dbg.txz distfile

[lwhsu]

Summary

Build tests-dbg.txz distfile which contains the test binaries with
debug symble. It is useful for debugging failing test cases.

[cem]

With the caveat that I am unfamiliar with this part of the build, looks reasonable to me. (And I am supportive of the objective.)

[gjb]

Has it been confirmed that the tests-dbg.txz file in fact contains files? I removed it from the list of EXTRA_DISTRIBUTIONS in r278486 because it resulted in an archive that did not have any content.

[ngie]

The changes are great!

Minor request: please fix the spelling errors in the proposed commit message before committing.

[ngie]

In D22272#486919, @gjb wrote:

Has it been confirmed that the tests-dbg.txz file in fact contains files? I removed it from the list of EXTRA_DISTRIBUTIONS in r278486 because it resulted in an archive that did not have any content.

Hmmmm... if so, that needs to be fixed :(.

[lwhsu]

In D22272#486919, @gjb wrote:

Has it been confirmed that the tests-dbg.txz file in fact contains files? I removed it from the list of EXTRA_DISTRIBUTIONS in r278486 because it resulted in an archive that did not have any content.

Yes, I have tested before and reconfirmed again. I didn't check which revision makes it contains right files, but I did a clean build and test-dbg.txz contains files as https://gist.github.com/lwhsu/daa0fca8c3ff59127e0632ade3e0523a

[gjb]

tests-dbg.txt586 BDownload

I suspect you will also want to include this for bsdinstall(8) then.