Improve libdeflate's worst-case performance decompressing malicious
DEFLATE streams by about 14x, bringing it within a factor of about 2x of
zlib, by skipping rebuilding the decode tables for the static Huffman
codes when they're already loaded into the decompressor.
This improves performance decompressing a stream of all empty static
Huffman blocks from about 0.36 MB/s to 175 MB/s, or the original
reproducer given on the Github issue from about 3.3 MB/s to 219 MB/s.
A regression test is added for these cases as well as the empty dynamic
Huffman blocks case to verify worst-case performance comparable to zlib.
Resolves https://github.com/ebiggers/libdeflate/issues/33
Move the x86 and ARM-specific code into their own directories to prevent
it from cluttering up the main library. This will make it a bit easier
to add new architecture-specific code.
But to avoid complicating things too much for people who aren't using
the provided Makefile, we still just compile all .c files for all
architectures (irrelevant ones end up #ifdef'ed out), and the headers
are included explicitly for each architecture so that an
architecture-specific include path isn't needed. So, now people just
need to compile both lib/*.c and lib/*/*.c instead of only lib/*.c.
