fix: build tests need libcrc.la

Build tests are failing because the need crc32c.cc's functions, so we
need to link them against libcrc.la

Signed-off-by: Roald J. van Loon <roaldvanloon@gmail.com>
Merge pull request #572 from roaldvanloon/wip-fix-buildtests

fix: build tests need libcrc.la

Reviewed-by: Sage Weil <sage@inktank.com>