Configure: Moved CXX11 requirement to --with-online conditional
This is to address issue #169 (closed).
The C++ 11 requirement was added to configure.ac in commit 56007723. Since CODES builds just fine without C++11, it seems like this requirement was added for support of SWM workloads which aren't built unless --with-online= is specified. So this requirement has been moved to reside within that conditional so that certain legacy machines that may not have updated to the 8 year old standard yet can still compile CODES without complaint if they don't need SWM.