cmake: compile crimson-auth with crimson::cflags

cmake: compile crimson-auth with crimson::cflags

* move auth related stuff into crimson/CMakeLists.txt, so we can
  link them against crimson::cflags, which populates the necessary
  definitions and other cxx flags when building these source files.
* expose crimson::cflags as a public library of crimson, as
  crimson-osd links against crimson. and the cflags should be populated
  to crimson-osd, otherwise they are compiled with different compiler
  options.

Signed-off-by: Kefu Chai <kchai@redhat.com>