fix Issue 11203

- fixup #614 - disable finalization for extern(C++) classes

- BlkAttr is already default initialized to BlkAttr.FINALIZE
  so we have to clear the bit for C++ classes.
Merge pull request #633 from dawgfoto/fix11203

fix Issue 11203
remove redundant BlkAttr declarations

- use core.memory.GC.BlkAttr
- add private BlkAttr alias to replace declarations
- replace BlkAttr.ALL_BITS with ~BlkAttr.NONE
Merge pull request #634 from dawgfoto/blkAttr

remove redundant BlkAttr declarations