Some of the autoconf logic is originally from Asad. In addition, the
explicit call to __gcov_flush() is now vendored in vdef.h like other
toolchain abstractions.

Similarly to how the ASAN setup was split in two steps.

Spotted this unusual construct while sweeping through the sanitizer flags.

Instead of referring to them for every single binary we build... While
at it we shouldn't need to add -fsanitize=stuff to LDFLAGS, and we
didn't in some cases. That should lead to smaller lines when running
make with V=1 or when silent rules are disabled.

To avoid repetition and very long lines.

Removing unused *SAN_*FLAGS variables and making sure to quote anything
that may be relevant to quote. Hopefully indenting in more readable way.

Fixes: #3634

Previously we would read the response Content-Length from a failed oc,
which would make the error response valid. Now, if this is detected,
we don't touch the Content-Length.

With the synth->filters koncept out of the picture this becomes
possible.

Fixes: #3441

Closes: #3318

Renovate `-n` and `-a` manual page descriptions

Fixes: #3672

After the removal of VSB_new() and VSB_delete().

Refs 5884e2f2

This will hopefully silence our continuous integration complaining way
too often about server leaking what http_process_cleanup() should take
care of.

The nested while loop made more sense when the surroundings were more
complicated.

Better diff with the --ignore-all-space option.

All call sites pass a non-null char pointer.

There might be linker flags that cat would fail to find.

Otherwise we always try to rebuild vrt_test when running make.

Spotted by Simon Vikström.

Closes #3671