Split Q_COMPILER_DEFAULT_DELETE_MEMBERS

Split Q_COMPILER_DEFAULT_DELETE_MEMBERS

Based on reviewer comments on
https://codereview.qt-project.org/#change,25992, split
Q_COMPILER_DEFAULT_DELETE_MEMBERS into
Q_COMPILER_DEFAULT_MEMBERS and Q_COMPILER_DELETE_MEMBERS. Clang provides
2 separate feature checks for these, all other compilers always define
both.

Keep the Q_COMPILER_DEFAULT_DELETE_MEMBERS define, though, for any
existing code that may be using it.

Change-Id: I8969e10989c776a822da153152cfecb99dda8cb9
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>