OS checks with configuration time DLOPEN_NEEDS_LIBDL

[Richard PALO]

> Change subject: Add DLOPEN_LIBS to configure for some cases where -ldl is needed use std::sqrt in vcldemo.cxx
> ......................................................................
> 
> 
> Patch Set 9: Verified+1
> 
> Build Successful 
> 
> http://ci.libreoffice.org/job/lo_gerrit_master/7482/ : SUCCESS
> 


-- 
Richard PALO