C++14 deprecation macro support
[[deprecated]] in C++14 mode. However, this does not mix well with
__attribute__ for export macros. Compiler-specific export attributes may be required. This is best done as a fix to
GenerateExportHeader.cmake and upstreamed to CMake (VTK can carry the patch though).
If export macros can't be fixed before 9.0,
[[deprecated]] should not be used until it is.