xz (but not xzdec) will normally warn about unsupported check
but since we are testing specifically such a file, it's better
to silence that warning so that it doesn't look suspicious in
test_files.sh.log.
The use of -q and -Q in xzdec is just for consistency and
doesn't affect the result at least for now.
This isn't perfect as the scripts can still fail if only
certain filters are disabled. This is still an improvement
as now "make check" has better behavior when all encoders
or decoders are disabled.
Grepping ../config.h is simple and fairly clean but it only
works if config.h was created. CMake builds don't create
config.h but they don't use these test scripts either.
Thanks to Sebastian Andrzej Siewior for reporting the problem.
Thanks to Jia Tan for the original patch which grepped xz
error messages instead of config.h.
I suspect that I used these in the original version because
Autoconf's manual describes that such a trick is needed in
some specific situations for portability reasons. None of those
situations listed on Autoconf 2.71 manual apply to these test
scripts though so this cleans them up.
This test fails before commit 18d7facd38.
test_files.sh now runs xz -l for bad-3-index-uncomp-overflow.xz
because only then the previously-buggy code path gets tested.
Normal decompression doesn't use lzma_index_append() at all.
Instead, lzma_index_hash functions are used and those already
did the overflow check.
Hiding them makes no sense since normally there's no error
when testing the "good" files. With "bad" files errors are
expected and then it makes sense to keep the messages hidden.
