When UBSan is enabled the equivalent flag is already added to the link
options and the UBSan runtime gets linked in, but when enabling ASAN
the build fails because it can't find a lot of symbols. The fix is to
link it if you use it.

ASAN_OPTIONS is a runtime environment variable and doesn't affect
compilation (unless exported as the symbol __asan_default_options,
which it isn't here).

Also note that enabling detect_leaks breaks macOS since AppleClang
doesn't support this (though the LLVM from brew does).

unit makes use of streamvbyte_isadetection.h which is in an internal
header not in the public API.

These are useful when loading untrusted data since it's typically
trivial to change the uncompressed size that's stored alongside the
encoded data. Doing so can cause the decode functions to read past the
end of the input data, which at best generates bad output and at worst
causes crashes if it happens to read into an unmapped page.

These presumably always passed so were never printed.

Also include the iteration for easier debugging.

The encode functions return size_ts so we should match that.

All the data would be about the same value [gap-1, gap+6] and wouldn't
border on a byte width meaning that all of the keys would be the same
and hence wouldn't catch bugs when reading the wrong keys. Instead use
the gap to space the elements apart.

AppleClang 16 doesn't appear to be clever enough to transform the loop
into a branchless one, so help it out by adding a loop that it knows
how to unroll.

Also do the same for streamvbyte_validate_stream_0124 though I haven't
tested the performance of that.

Nothing fancy, just processing 4 keys per vector. In both micro- and
macro-benchmarks this performs at basically the same speed as the loop
added in the previous commit (tested with clang), both of which are
significantly faster than the original version.