util: Add crc32 implementation
a05d4213f0f9 ("Add 'gen-dhchap-key' command") introduced the zlib
dependency in order to use the crc32 function. This simple function
alone is a not worth the additional dependency, so let's ship our own
crc32 function.
The implementation is from teh elfutils project which is licensed under
LGPL 3 or later of GPL 2 or later. For this project we choose the GPL 2
or later license.
Link: https://sourceware.org/git/?p=elfutils.git;a=blob;f=lib/crc32.c;hb=575198c29a427392823cc8f2400579a23d06a875
Signed-off-by: Daniel Wagner <dwagner@suse.de>