tests: Avoid shell limitations in huge input tests.

tests: Avoid shell limitations in huge input tests.

It seems that the very large here-documents used in the excessive
specifier/declarator tests can be problematic on some ksh versions.

Normal compression tools handle this data very well, so instead of
using the shell to generate it it should be just fine to just use
gunzip to do this and skip the tests if that cannot be done for
whatever reason.