libbb: introduce and use common crc32 routine

libbb: introduce and use common crc32 routine

function                                             old     new   delta
crc32_block_endian1                                    -      37     +37
crc32_block_endian0                                    -      34     +34
global_crc32_table                                     -       8      +8
file_read                                             82      87      +5
gzip_main                                            211     214      +3
xz_crc32                                              40      35      -5
crc32_table                                            8       -      -8
calculate_gunzip_crc                                  54      34     -20
lzo_crc32                                             54      25     -29
cksum_main                                           298     211     -87
------------------------------------------------------------------------------
(add/remove: 3/1 grow/shrink: 2/4 up/down: 87/-149)           Total: -62 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>