[Minor] Fix Sophos ENCRYPTED caching

[Minor] Fix previous commit

[Minor] dkim_signing: auth_only is a misnomer (#3230)

[Minor] Fix spamtrap score

Issue #3162

[Minor] Fix Debian reproducible builds

* The `CMAKE_BUILD_TYPE=None` option is commonly used to respect the
  user's optimization flags. Users may be interested in enabling LTO
  anyway in that case. Implement this the Debian build.
* Remove typo, the value is called RelWithDebInfo. Enable LTO for this
  by default.

* Use the install RPATH to avoid relinking at install time.
* This additionally ensures reproducible builds invariant of the build
  directory since build paths such as `X/src:X/contrib/replxx:...` are
  no longer embedded in the binary.
* This assumes that binaries are not ran at build time. If this is
  needed, CMAKE_BUILD_RPATH_USE_ORIGIN=ON can be used instead (requires
  CMake 3.14). For older CMake, try setting LD_LIBRARY_PATH.

* Use relative paths for `#line` directives to allow reproducible builds
  independent of the absolute build directory. For /b/rspamd/src/x.rl
  and build dir /b/build, it could result in `../../build/src/x.rl`.
* The `-L` option for `Inhibit writing #line directives` is useless, it
  just comments out the line with `/* ... */`, but that means that the
  source file is still different.
* Note that ragel only accepts one input file, despite plural `INPUTS`.

* Reproducible build: avoid defining the BUILDROOT macro and avoid
  embedding the build directory in the test image. Instead rely on the
  test files being present next to the executable.
* I considered using g_test_build_filename, available since GLib 2.38
  (available on all supported platforms, RHEL 7, Debian, Ubuntu, etc.),
  but decided against it because it would require setting the
  G_TEST_SRCDIR or G_TEST_BUILDDIR environment variables. Therefore this
  patch simply parses argv0 directly.

* Reproducible builds! No more absolute paths in source files, so the
  generated binary is also invariant of the build directory.
* Output modules.h in snowball/libstemmer/ instead of snowball/. This
  allows removal of the extra include directory and -f option.
* This partially reverts some changes in
  d178f201fd
  and matches the commands in GNUmakefile.

* Avoid including the absolute header path to permit reproducible builds
  invariant of the build direvtory.

* Enable -ffile-prefix-map to ensure that assert statements in
  contrib/libev/ev.c and other places do not store the full file path.
  This ensures reproducible builds, invariant of the build directory.
  Supported since dpkg 1.19.1, including Debian buster and Ubuntu 19.04.
* Enable all hardening features while at it, this adds bindnow only. See
  https://manpages.debian.org/buster/dpkg-dev/dpkg-buildflags.1.en.html

Remove .PHONY marker for consistency. Move override_dh_strip before the
target dh_makeshlibs as is is executed right before that.

* glib 2.28 is the current minimum declared in CMakeLists.txt, but even
  Jessie satisfies that requirement. Remove it.
* Use DEB_HOST_ARCH for "The Debian architecture of the host machine"
  instead of DEB_TARGET_ARCH which is relevant for cross-compiling only.
* Update luajit arches based on https://packages.debian.org/sid/luajit
  * Added arm64, mips64el, ppc64, ppc64el (stretch-backports / buster).
  * Removed kfreebsd-i386 and 32-bit powerpc (removed in Jessie).
  * Removed powerpcspe (unofficial port with outdated luajit).
  * Maintained mips (removed after buster).

[Minor] Simplify creation of dist tarball that is reproducible

Bring Debian packaging up-to-date