cmake: avoid duplicate symbols

cmake: avoid duplicate symbols

Some symbols from the crc32, arch and fmt libs
are re-exported by libceph-common:

  FAILED: bin/unittest_time.exe
  ld.lld: error: fmt::v9::format_error::~format_error() was replaced

llvm throws errors because of the duplicate symbols.
One workaround is to use objects instead of static libs
for the libs. For libfmt we'll use the header-only version.

Signed-off-by: Lucian Petrut <lpetrut@cloudbasesolutions.com>