... but we can not make any assumption as to why

Fixes #3664

Trying to unconfuse bmake on FreeBSD:

    make[6]: don't know how to make vsl_glob_test_coverage. Stop

But I can't reproduce it locally with bmake on Linux.

Instead of generating a test script that performs the compilation, we
can give automake a no-op linker command. With that vrt.h is verified
with a simple `make` or `make all` invocation, before `make check` even
kicks in.

Doing it this way also gives applicable warnings like strict-prototypes
a chance to fail earlier.

Refs #3667

One can always run `make -C include/ check VERBOSE=1` for feature
parity, and even get the other goodies from the regular test driver.

It should be more friendly to maintain than a script incrementally
generated by a makefile. Make it responsible for also running
vsl_glob_test without arguments instead of the test driver, and
restore its output. In case of failure, the -x mode should help
figure which vsl_glob_test failed. While at it give the script a
proper shebang.

Refs #3667

Something DNS always breaks when I join a new network.

After 88698015 broke 32 bit, we need to adjust the default(s) which
are special cased for 32 bit in mgt_param.c. Instead of increasing
things, we make sure the old default vsl_buffer of 4k is maintained.

This looks like a copy-pasta or autocomplete mistake.

On many busy production systems, the VSL buffer for transactions often
fills up, triggering a flush to the VSM. If such a transaction takes a
long time, it can happen that the flushed data is overwritten before
the whole transaction completes. The result is that these transactions
are missed by varnishncsa and other tools. Increasing the vsl_buffer
does the trick, at some cost in workspace usage.

The cost implies that one should increase the workspaces, too. Since
the old defaults of 64k each are too low for many common use cases
today, it is natural to increse everything in one patch.

Some test cases have been updated. These are all cases where the
workspaces have been set very low, and to make sure we are still
testing the same regression, the vsl_buffer has been set to the old
default instead of increasing the workspace.

Spotted by flexelint.

This is how I found the accidental bug fix for #3662:

    git show varnish-6.0.8:bin/varnishtest/tests/c00053.vtc >bisect.vtc
    tools/vtc-bisect.sh -g varnish-6.0.0 -j32 -i

I hope this will help others, I use this script whenever the cause of a
failure is not obvious.

Spotted by flexelint.

Do it on demand, so start/stop changes to available commands is properly reflected.

Fixes: #3642

We need to ensure that vmods use the same functions and data
types as varnish-cache.

Also it seems that having the define in autoconf might suggest
that it could be changed, which would be misleading.

For now, this is only VRE_unpack() to get the pcre2_code handle.

If we ever change the regex backend again, we will remove
vre_pcre2.h and add something else.

Suggested by Dridi, thus authorship attributed to Dridi.

Refs 31e3895a

Adapted to the pcre2 change, and (manually) tested both with and
without jit compilation and various tweaks to trigger both match
and depth limits.

Closes #3658

Before 6014912e, VRE_sub() used an
ovector of size 30, which always containted sufficient space to store
the 10 possible back- references \0 thorugh \9.

Now that we use pcre2_match_data_create_from_pattern() and later
pcre2_get_ovector_pointer(), we only get space for the number of
substrings in the pattern, see pcre2api(3):

	The ovector is created to be exactly the right size to hold
	all the substrings a pattern might capture.

Consequently, we need to check that back references do not exceed the
maximum ovector.