Fixed compilation with compilers not supporting AVX2.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84191 b8fc166d-592f-0410-95f2-cb63ce0dd405
Fixed compilation with compilers not supporting AVX2.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84192 b8fc166d-592f-0410-95f2-cb63ce0dd405
Disabled syslog sink when neither Boost.ASIO nor native syslog API are available.

git-svn-id: http://svn.boost.org/svn/boost/trunk@84193 b8fc166d-592f-0410-95f2-cb63ce0dd405