Use a constant for the suffix for indirect symbols.

symconst.pas:
  + add indirect_suffix constant
symdef.pas:
  * tstoreddef.rtti_mangledname: use indirect_suffix
  * tobjectdef.vmt_mangledname: use indirect_suffix
  * tobjectdef.rtti_mangledname: use indirect_suffix

git-svn-id: http://svn.freepascal.org/svn/fpc/branches/svenbarth@28640 3ad0048d-3df7-0310-abae-a5850022a9f2