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fixes #615

The other `#ifdef HAVE_*` were moved in switches,
so that they don't rely on being the last before `default:`

The tests needed fixing up cases of using GOST as invalid values.

fixes: #573

See m4/knot-version.m4

Still there are some problems with clang on 32-bit systems, so the atomic
functionality is no longer required for such systems (statistics or mod-cookies
might work slightly wrong).

Implements initial support for continuous fuzzing with [google/oss-fuzz](http://github.com/google/oss-fuzz). Changes:

- Removes `--with-santize-coverage` config flag: the clang6 `-fsanitize=fuzzer-no-link` replaces this
- Adds `--with-oss-fuzz` config flag: links `-lFuzzingEngine` into fuzz targets
- Adds logic to `make check` that runs the fuzz targets with a single seed input to ensure they exit successfully