insane.bbclass: Avoid libdir QA check if PACKAGE_DEBUG_SPLIT_STYLE='debug-file-directory'

If PACKAGE_DEBUG_SPLIT_STYLE='debug-file-directory', debuglibdir will be
"/usr/lib/debug". Usually 64bit libs should be put under "/usr/lib64".
This often cause an warning, so skip the checking.

Signed-off-by: Jian Liu <jian.liu@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>