Test the kernel build with the standard warnings enabled so that we
don't miss issues like fixed in PR #2802.

Stacked on top of PR #2802 so CI passes, so it includes the fix. But, I
won't merge until it is merged, so @solbjorn gets the credit for the
fix.

[contrib][linux] Fix build after introducing ASM HUF implementation

[lib] Make lib compatible with `-Wfall-through` excepting legacy

[build] Fix oss-fuzz build with the dataflow sanitizer

Fix typo

The dataflow sanitizer requires all code to be instrumented. We can't
instrument the ASM function, so we have to disable it.

minor: constify MatchState* parameter when possible

Switch to a macro `ZSTD_FALLTHROUGH;` instead of a comment. On supported
compilers this uses an attribute, otherwise it becomes a comment.

This is necessary to be compatible with clang's `-Wfall-through`, and
gcc's `-Wfall-through=2` which don't support comments. Without this the
linux build emits a bunch of warnings.

Also add a test to CI to ensure that we don't regress.

turns out, it's possible to constify MatchState* parameter
in some parts of the binary tree algorithm,
making it a pure read-only parameter,
as opposed to a mutable state.

This is supposed to be helpful for both maintenance and the compiler.

The mentioned path is being created/used by the 'import' rule for
generating source files for Linux kernel.

Signed-off-by: Alexander Lobakin <alobakin@pm.me>

Commit a5f2c455 ("Huffman ASM") added a new ASM source file,
but it wasn't added to the kernel Makefile despite that it received
support for Huffman ASM according to the internal definitions. This
leads to undefined references, as huf_decompress.o now calls those
ASM functions.
Add it to the list of sources when building inside the kernel tree.
Kbuild can handle .S files just fine, so none additional rules
needed.

Fixes: a5f2c455 ("Huffman ASM")
Signed-off-by: Alexander Lobakin <alobakin@pm.me>

Linux 5.15 introduces a new Kconfig option, CONFIG_WERROR, which
forces -Werror for the entire kernel.
Current in-kernel ZSTD implementation uses functions deprecated
in 1.5.0, and thus fails on -Wdeprecated-declarations.
Turn this particular error into warning to be able to build the
kernel with CONFIG_WERROR. I'm not disabling them completely to
make sure they'll be visible and [hopefully] fixed sooner or later.

Signed-off-by: Alexander Lobakin <alobakin@pm.me>

Reduce stack usage of block splitter

[contrib][linux] Reduce stack usage by 80 bytes

Instead of calling `ZSTD_compress_advanced()` and
`ZSTD_initCStream_advanced()`, which each take a `ZSTD_parameters` by
value, use the new advanced API.

Stack usage went from 2024 -> 1944.

[contrib][linux] Fix up SPDX license identifiers

Minor documentation update

Correctly identify that we are GPL v2+ or BSD 3 clause, as pointed out
in issue #2663.

to mention ripgrep alternative which transparently supports zstd-compressed files.

using ronn-ng

notably as a way to overcome shell expansion limitations,
notably in a scenario of dictionary training.

Fix NCountWriteBound

Use new paramSwitch enum for row matchfinder and block splitter

[huf] Fix compilation when DYNAMIC_BMI2=0 && BMI2 is supported

* Fix compilation issues pointed out in PR #2790.
* Add test cases to GitHub actions that test all combinations of
  `DYNAMIC_BMI2` BMI2 support.

Assembly implementation of 4X1 & 4X2 Huffman

[fuzzer] Add Huffman decompression fuzzer

add msvc2019 to build.generic.cmd

Add a fuzzer for Huffman decompression. Fix several bugs in Huffman
decompression, mostly related to `op == NULL` and pointer underflow.

[build] Add support for ASM files in Make + CMake

* Extract out common portion of `lib/Makefile` into `lib/libzstd.mk`.
  Most relevantly, the way we find library files.
* Use `lib/libzstd.mk` in the other Makefiles instead of repeating the
  same code.
* Add a test `tests/test-variants.sh` that checks that the builds of
  `make -C programs allVariants` are correct, and run it in Actions.
* Adds support for ASM files in the CMake build.

The Meson build is not updated because it lists every file in zstd,
and supports ASM off the bat, so the Huffman ASM commit will just add
the ASM file to the list.

The Visual Studios build is not updated because I'm not adding ASM
support to Visual Studios yet.